Nice

sloan here are a few recommendations for boutiques

http://www.nicegardenhotel.com/nice/hotel/en

http://www.hotel-le-geneve-nice.com/en

You could try the Windsor, which is often recommended. However, given the Mobility restrictions you might instead go for one that is close to a tram stop. The two tram lines (both should be open, at least to the center) are very convenient to mount and take, and are quite frequent (compared to the bus). I'd look around the Place Massena stop, the Victor Hugo Stop (near the Boscolo Excedra -- a large hotel but with an upscale, elegant feel. Also this stop is walkable to some of the others mentioned previously), or near the Opera (perhaps Les Suites Massena), or Cathedral stops at the edge of old town (fewer high end choices, but convenient. Make sure the hotel has an elevator). These stops will also keep you close to a good collection of restaurants as well. You could also try one of the hotels along the Prom (La Perouse), but then you'll need to keep an eye on the distances and use buses/Uber.

sloan,

I not sure if this meets your criteria but you might have a look at this hotel - https://www.hotel-nice-suisse.com/ . It's at one end of town and not far from the Promenade des Anglais. Some rooms have incredible views over the beach.