I love the Eifel Tower area which is close to Rue Cler. I also have some mobility issues, but don't use a chair. Yet. I went to Paris alone last year with my 11 year old grand daughter and stayed at Hotel Eber Mars. The elevator is very, very, small, though, so I don't know if your wife will be able to ride it standing, but it probably won't fit the chair. The owner of this hotel is so very kind and helpful, and he gave very good advice: He told me to buy the ticket for the "red-line" hop on hop off bus, and that way we could see the entire city, and only get off at the sites we wanted to see. This bus covered ALL of Paris, while the yellow one did not. My Grand daughter got a kick out of riding under the Arch du Triumphe (sp), we got off at Champs Ellyse (I am so sorry for the bad spelling, I speak Spanish and some Italian, no French!) I'm pretty sure they will accommodate the chair, but ask Mr. Eber-Mars when you call.
This hotel is within walking/pushing distance for you to sit on the bench in the park and watch the Eifel Tower light up every night. The park is beautiful.
Rue Cler (Rick S.' favorite street) is just one block away, as is the big Invalides square, military museum, etc. Lots of cafes, and
you just can't beat walking down this street past the flower stands, vegetable stands and charming restaurants. There are inexpensive and very high quality pizza places near as well as cafes with outdoor seating.
I don't know if my hotel suggestion will work for you, but I liked this area for me and my difficulties. You can call the hotel and
ask them about the chair, and if they have a place to store it at night. The owner is wonderful, and speaks perfect English. Make sure you speak to him. There is another hotel on this street, Hotel Bourdonnaise (sp). I think it may be more expensive, though.
Also the hotel is very close to the boats that go down the Seine river (Also hop on hop off) which will allow your beautiful wife to see all of the beautiful bridges and scenery, and won't involve a lot of walking.
You sound like a delightful man and I hope you and your lovely wife have a fabulous trip to the City of Lights! Sleep late, and stay up late to see those lights! We did, and I was with my little princess. I will never regret it! Paris, as a city, is a good choice, because unlike many other places it's pretty flat!