Accessible European City

Would love some advice/recommendations for travel with mobility issues. My husband and I would like to take a trip to a European city for 5/6 days this fall. The issue is my husband has MS and uses walking sticks. He can still walk but he is very slow and uneven surfaces are difficult. Every time I try to plan something I get stuck. It seems there are plenty of ideas for fully mobile people and for wheelchair bound people but not much for people “somewhere in between”. We use a wheelchair to get through airports but don’t own one. Is there a city that is more accessible than others? Are riverboat cruises out of the question? Do tourist attractions generally have wheelchairs available to rent? Mostly would love advice/recommendations/encouragement from anyone who has been in the same position.