We have done 4 river cruises 17 Ocean cruses and lots of bus tour, rail trip, auto rental trips and more.
It is best to see Ireland renting a car. Some car rental companies may not rent to someone 75 years old. You can probably find a bus tour of Ireland, there are lots of British travel firms lake Trafalgar that are excellent.
For river cruises, I always look at 4-5 different companies.
Avalon is one of the higher priced firms that is excellent, but their price is just too much every time I look at them.
Uniworld is another higher priced firm that has prices over what I want to pay.
Viking is an excellent line and their prices a more competitive, but their ships tend to be a bit larger than others. Still Viking is one to compare.
AMA Waterways is excellent and more in a class with Avalon, but their prices have gone up in recent years. We did one cruise with them and loved it, but now find their prices to be not as competitive.
Vantage World Travel offers excellent river cruises and we have done three trips with them than included a river cruise. All were excellent and Vantage was the best price. I strongly recommend taking a look at Vantage.
Grand Circle is another company that offers river cruises. They tend to be close to Vantage in pricing.
If you want a budget river cruise Gate 1 is the real thing. They offer river cruise with more optional tours and their ships have more of a budget feel, but their prices are amazing. I have never picked them, because the would be the equivalent of a Motel 6 vs. a Marriott, Sheraton or Hilton.