Trip of a Lifetime

Wow, what an adventure. Without knowing what you like (city vs countryside, art/museums vs connecting with locals), it's hard to advise. If you are set on adding one more country, I'd suggest Italy just to round things out, since you anticipate this is your single Europe trip. Especially since this is your first time overseas, I'd suggest alternating big city and small city locales, to help prevent burnout. Plan a no-plans day at least once per location, to wander, rest and unwind.

If you are open to rethinking your big plan, consider that moving cities involves travel days, and again, the risk of burnout if you've never traveled like this before. How is your endurance? Have you traveled away from home for this long in your home country? A less strenuous alternative could be, for example, London, then Scotland OR Ireland, then two weeks in France, then the cruise. And finally, if possible, consider that you COULD return at a future date. This reframing helps you relax when you are there and not try to cram everything in.

Have you already looked at the weather averages for your proposed locations in March? While weather won't make a great deal of difference in the large cities, it could wreak havoc with day trip plans. Ireland and Scotland can be cold and wet, with the possibility of snow in the highlands at that time of year. It may be more prudent to start with somewhere somewhat warmer and drier, like the south of France, and work your way north. Put Britain at the end of your trip, not the least because you will sail from Southampton, so why pay extra for backtracking. Your time in Europe is vague. How many weeks altogether are you planning on?

You need to be strategic regarding where you are the week before and after Easter, which is early in 2026. The popular places will be extra crowded then, and some businesses closed Easter Sunday and Monday.
Also, you could fly multi-city, into one city and out of another, if you can still change flights.
March and early April are a bit early for gardens, so plan accordingly. However, the middle of April is great for tulips in the Netherlands, so I submit that for consideration.
Plan on extremes in weather at that time of year- one day spring, the next winter, and rain anytime. The proper clothing will contribute to a better trip.
Have a great time.

Also think about how you will travel between countries. From London, you can take a train to Scotland. From Scotland, you can take a ferry to Ireland. From Ireland, you can take an overnight ferry to France. These take time, of course, but might be more relaxing than flying. I think your plan of one-week stays with day trips is fine for the UK and Ireland, but France is so much bigger. I would consider a week in Paris and a week somewhere else (depending on your interests, maybe Nice, Strasbourg, Bayeux?). You haven't said how many weeks total you will have for the trip or what your interests are, so it's hard to know what to add, but I'll put in a plug for Amsterdam (probably don't need a week there). Are you sailing home from Southampton?

Have you already looked at the weather averages for your proposed locations in March? While weather won't make a great deal of difference in the large cities, it could wreak havoc with day trip plans

I agree with CJean—I was in England for almost 6 weeks from mid-March to almost mid-April in 2024, and the first half was filled with rain and flooded roads and closed sights. Also, as suggested above, I think that choosing just one or two countries in the UK would probably work better for you. Then you could move onto France, but I do love KC's idea of adding Italy in there. It's a wonderful country and would be a shame if you went to Europe and missed it.

Are you planning to rent a car while you are there, or rely on public transportation? That would definitely affect your base in each country, and if you are relying on public transport, you would do best staying in a city or a larger town where you can easily take trains and buses to your day trip destination.

It would also help to know your interests. You mentioned health issues, but do you/are you able to walk on short hikes? Do you enjoy museums? Castles? Coastal towns on the sea? Forests? Food? Art? I'm not trying to confuse you but if you want this to be the trip of a lifetime, then it should really focus on your interests and what you want to see.

I would not fret too much over it. The beauty is that it will be your first time Europe and thus EVERYTHING is new. Could you really go wrong?
Start your planning on each place you have listed. Find the cities you want. Easy to find out what people see in each area. Get your guide and Viator will pop up in searches for day trips from various cities. You need not do them, but it gives you ideas you might otherwise not know.
Unfortunately these forums may give you anxiety because you will get all sorts of suggestions and may start some major FOMO.

So where should we go for our remaining time.

How much time is that?

Joe,
Reading your posts I get the idea you have all of March and April, or about 8 weeks before the QM2. Is that correct?
Weather in March and April suggest to me to begin in the south...Italy. With what appears to be 8 weeks I would begin with Rome for 7 days, then 4 days in Florence, then the French Riviera (Nice) for 4 days, then Paris for 7 days. Belgium and the Netherlands 6 days total, Ireland 7 days, Scotland 7 days, London 7 days. That comes to 49 days. Add in travel days between locations (some half days, some whole days) and you have another week, or about 8 weeks total. You wind up in London so not far from your embarkation point. And you will have warmer weather in the south at the beginning of your journey.
Each of your locations could feature day trips to get out of the city (e.g. Pisa from Florence, Villa d'Este from Rome, Windsor from London), And Ireland is small and distances are short, so you could easily move around the countryside there. I haven't been to Scotland, but I am guessing it is similar there. Likewise the Netherlands and Belgium.

This is just a suggestion. You can decide on where you want to go based on your likes/needs/wants. You will have a wonderful time!

(By the way, my husband sailed on the QM1 in the early 60's, steerage class. It was very cheap, but the ship was segregated by class back then and lots of areas were off limits to the hoi polloi. Before that, as a child, he made three transatlantic crossings on some French Line ships. He also went with the US army in the 60's, five hammock beds in a group, one above the other. There weren't the stabilizers back then that they have now, and he was one of the few who didn't get seasick. It was quite the adventure! Steerage looked pretty good to him after that trip!)

The QM2 will be heaven! Bon Voyage!

Is the QM2 sailing out of Le Havre, France, and can you confirm how many total nights you will have (is it about 8 weeks?). Also, can you give some suggestions of what you enjoy? Otherwise, I like the idea of beginning in the south (i.e., Italy) and making your way north. Do Rome, Florence, Venice, somewhere in Germany on your way to Amsterdam (to enjoy the tulips blooming), then fly to Ireland, to Scotland, down to London then Paris to then make your way to Le Havre for the voyage home. It would also be helpful to know what a "moderate budget" is. Moving around costs more, so if budget does not allow for that, best to find a spot in each of the four countries you noted and do day trips. Let's take Ireland for example, what are you hoping to do there because it would be very easy to fill two weeks just in that location (and the other three that you mentioned).

I like Judy's itinerary except I would not go to Belgium and add that time to England-maybe go to York or Cardiff Wales.

Given a "moderate" budget, I'd strongly suggest considering Prague. It's one of the world's greatest cities, it is completely different from the other places you plan to visit, and perhaps best of all it's inexpensive. The architecture and culture are just amazing, and if you're there in summer it will be possible to choose from a variety of music concerts and opera performances. Finally, if one or both of you enjoys beer, it's a slam dunk.