I have two large dogs and a parrot. The parrot and cage live on the dinette table. The dogs spend a lot of time in the cab seats watching everything that is going on. That helps a lot as I don't have them underfoot constantly in the small space. I have a 21ft Class C. I use the cabover bed for sleeping and the dogs sleep up there also (they love the view).
With a bad back, you will probably want a corner bed for you. Do your cats prefer high places? With a Class C that has the cabover, you could use that space for storage and leave room for the cats to have a high safe spot in the RV. You could even take out the mattress up there, put a couple cat beds and the litter box in its place (lay linoleum over the plywood), and make a "tailgate" that you can lock upright to keep the cats secured if you worry about them escaping out the door.
A small B often does not have a dedicated bed, so you would have to convert a sofa or dinette. A 24ft class C, should have a corner bed. Making the bed can be a problem with a corner bed, but if you have casual bedding you can usually make it work.
As others indicate, the height can be an issue if you're using it as a daily driver and need to use parking garages, etc. With your bad back, are you unable to walk distances? Do you need to use the handicap parking spots? If so, you may find it difficult to park anything longer than 21ft in the handicap spots - many will be right up against the sidewalk so you can't back in and let the rear end hang over and beyond the dedicated space. Widthwise, you may be OK if you park where there is the extra space for wheelchairs.
If you don't need to use handicap parking, then you should be OK with up to a 24ft rig without much issue. Just park further out where you can fit in 2 spots side by side and back the rear so it overhangs a planter, etc.
For maintenance, you may end up needing to adjust your grey/black tank valves. My black valve was under the chassis (the grey was just at the edge). I ended up moving the black valve out to the same level as the grey so I wouldn't have to bend down under the vehicle. Checking for water leaks should be easy, but you may need to have any leaks repaired professionally due to your back. Washing can be done at a truck wash for usually a reasonable fee.
A macerator might be a good investment. If you don't get a rig with one already built in, you can buy one for a couple hundred and find someone to install it.
As for parking the rig "at home", that will all depend upon where you buy. Many places that cater to a specific clientele (55 or over, golfers, etc.) are likely to have rules about what can and cannot be parked. Even though your rig would be your daily driver, the association will still see it as an RV. Get the rules before you buy. If you really want the RV, then plan on going through multiple places before finding one that will let you park the RV at home.
If you're just looking at the RV for the time you will be shopping for a home, then you might be able to sell it when you get your home and buy a car for your new daily driver.