I read your post and I was just so sad. I'm sure that there will be at least one river cruise itinerary that would work for you, but it will take a lot of research to look at all the possible combinations.
It might not be an easy trip, because many towns do have cobblestone streets, and are narrow, making it hard to use a wheelchair. The part of Amsterdam with the crescent shaped canals comes to mind right away. But most of Budapest should not be a problem.
I do NOT recommend staying on the ship! It's not like an oceanliner, because it has to be narrow enough to fit in a river. There will be nothing to do on the ship except maybe talk to some of the crew who stayed behind. If you are not confined to a wheelchair, you should not have problems getting on and off the ship or doing most of the excursions. The average age of river cruise passengers is older, so they should not be racing from place to place. If you go to a museum and are not up to walking around, you can probably get a chair near the door and rest up while more ambitious passengers check out more exhibits. Since you will be in Europe, there will be at least one church on the itinerary, and sitting is permissible there.
I checked out Avalon's website, and they do not go out of their way to welcome passengers with disabilities. I purposely checked theirs, because they are one of the better companies, and have roomier cabins. Here is what I found:
Travelers Who Need Special Assistance on Tours and/or Cruises:
"You must report any disability requiring special attention while on tour or on cruise to Avalon at the time the reservation is made. Avalon will make reasonable attempts to accommodate the special needs of disabled travelers, but is not responsible in the event it is unable to do so nor responsible for any denial of services by air carriers, hotels, restaurants, or other independent suppliers. Avalon cannot provide individual assistance to a vacation participant for walking, dining, getting on and off motorcoaches and other vehicles, or other personal needs. A qualified and physically able companion must accompany travelers who need such assistance and must assume full responsibility for their well being.
"Not all sightseeing stops/sites accommodate wheelchairs and some locations and sightseeing activities require extensive standing, sitting, or walking. Avalon is not responsible for any missed activities due to a participant’s inability to participate with the group. The Americans with Disabilities Act is only applicable within the United States and facilities for disabled individuals are limited outside its borders. Most transportation services, including the touring motorcoach, are not equipped with wheelchair ramps. Motorized scooters are not typically suitable on international tours.
"Although some of our ships have elevators, many of our small ships (e.g., river cruise vessels) do not. Passengers requiring ship elevators should inquire before making reservations. Additionally, most stateroom doors and restrooms are not wide enough to allow access by standard wheelchairs, and bathrooms and other doorways may be fitted with coamings. For safety reasons, passengers in wheelchairs cannot be carried on ramps in ports where the ship is at anchor."
I recommend you find a travel agent who likes making dreams come true, and let him/her help you.
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