I currently have to use two canes. Some museums, particularly the Louvre and Centre Pompidou, involve a lot of walking. Fortunately, several museums have wheelchairs to loan. Generally, you can't reserve them but I did not run into any problem by just showing up. You have to leave proof of identity — my photo driver's license worked fine. A copy of your passport may work. They keep your ID at the desk where you get the wheelchair (typically where you check backpacks) and give it back when you return the wheelchair.
Museums in this report do not charge admission for the handicapped person and one assistant. You might be asked for proof of disability, so take a copy of your handicap parking placard, government form or a letter from your doctor. Usually, if you're obviously challenged, such as using a wheelchair or a cane, they do not ask for proof.
Besides no admission charge, you do not need to wait in line. At every museum I visited (and the Eiffel Tower), the handicap entrance is the one for visitors already with tickets or for groups. Some are clearly marked with the blue wheelchair logo. Or look for “entrée prioritaire.”
Musee d’Orsay
The d’Orsay is large and a wheelchair definitely helps. It is reasonably easy to navigate but some of the accessible elevators are hidden behind doors with a handicap button to open, which gets you to the actual elevator door. Get a map and ask at the information desk near the entrance on the main floor.
http://www.musee-orsay.fr/en/home.html
http://www.musee-orsay.fr/en/espace-particuliers/private-individuals/disabled-visitors/welcome.html
Pompidou Centre
A wheelchair is particularly necessary for the Pompidou if you have mobility issues. A visit to the main galleries on 4 and 5 plus the restaurant on 6 can involve a lot of walking because the building layout and placement of the elevators is so poorly designed for accessibility. The Centre is a block long. The main elevators are near one end but the entrances to each floor are near the other end. For my visit, we traveled nearly the length of the building ten times!
https://www.centrepompidou.fr/en
https://www.centrepompidou.fr/Visite/S-informer-sur-l-accessibilite (use Chrome browser)
Musee de l’Orangerie
This museum is small but can take up to one or two hours to visit. Personally, I thought the galleries downstairs were more interesting than the famous Monet water lilies on the main floor.
http://www.musee-orangerie.fr/en/article/accessibility
Musee Picasso
Although a small museum in comparison to d’Orsay, the layout of the elevators makes you backtrack on most floors, so walking through exhibits twice. And it can take two hours or more if you don't rush through.
http://www.museepicassoparis.fr/en/accessibility/
Email: accessibilite@museepicassoparis.fr
Fondation Louis Vuitton
A new modern art museum designed by Frank Gehry. Not as large as d’Orsay, but a wheelchair is still helpful if walking long distances is an issue. A problem is that there are 3 elevators (east, west and central) but we found two of elevators would not go to some floors they were supposed to go to. Twice we had to go from the east elevator to the west (or central) to get to a particular floor because of defective elevators. http://www.fondationlouisvuitton.fr/en.html
http://www.fondationlouisvuitton.fr/en/accessibilite-du-batiment.html
Musee Marmottan Monet
This museum has 2 or 3 loaner wheelchairs. The elevator from the main floor to the Monet paintings on the bottom floor is large but the elevator to the upper floor is small and may not hold a wheelchair. This is a relatively small museum in a mansion, so if you can walk for an hour or so, you might not need a wheelchair.
http://www.marmottan.fr/mobile/page.asp?ref_arbo=2497&refer=
The Louvre A lot of walking. You can't see all in one day.
https://www.louvre.fr/en/accessibility