Charla, I think you've been give some really good advice. Without having taken one myself, Rick's tours are not for you if you don't want to do a lot of walking or manage your own bags. As someone said above, just about any escorted tour is going to involve a lot of walking and often visits to a fair amount of museums, churches, historic buildings, etc. As well, It is not unusual for historic centers to be largely pedestrian only, and some of them can be quite hilly.
Has anyone traveled with Bookingmundi.com?
Never heard of it and upon poking at the website, this jumped out at me on the Legal and Contracting Parties pages:
Bookmundi is not a party to the contract between you as a customer and
the supplier of the Product and therefore has not responsibility or
liability to you in respect of the terms of that contract whether
directly or indirectly.
All bookings are made with the supplier offering the Product in
question, not with Bookmundi. Bookmundi only facilitates the making of
the reservations with the suppliers of Products. Bookmundi is not a
party to the contract between you as a customer and the supplier of
the Product and therefore has not responsibility or liability to you
in respect of the terms of that contract whether directly or
indirectly.
This means that they are a 3rd-party clearing house that does not book or operate their own tours. Nope, not a service I'd use.
IMHO, given your situation the suggestion to look at river cruises is a really good one. You'd unpack once and would not have to deal with your luggage on a daily basis aside from getting to/departing from the ship (some will assist you with transfers). You do not have to take any of the included walking tours if you don't wish to, or may choose to leave them partway through if they're too much...although you would have to find your own way back to the ship. The same would be true in you decided to sightsee completely on your own. You likely will be able to navigate around the vessel without many stairs, unlike some European hotel rooms in old, historic-center structures, and enjoy a variety of scenery from the decks as you glide by.
LOL, both Rhine day-trip cruises I've done in Germany were overcast, windy and a bit wet but still scenic! You can't control Mother Nature, eh? As well, the boats only travel waterways that can accommodate them to begin with, and recent periods of drought have caused some to have to move their passengers from certain points to others via bus when parts of the rivers were too shallow. But all that aside, river cruises are as close as you're likely to get to type of trip you're looking for. Take a look at some of them?