The used C will get you more space for the dollar but the right B will do everything you want and can be parked almost anywhere. Many Bs are 20' or less and have all the features you want. True Bs are only as wide as a van. So called B+ campers are really just small Cs. If you wanted a full bathroom with shower you might have to go over 20'. Ours is 19' long and 8.5' high. At 6' I can stand up in most of it, has twin coaches that make a roughly queen size bed, with one person you could just use one coach either open or closed. Has a one burner stove, a small frig, microwave, sink and porta-poty.
We recently bought it used to replace our small popup 8' truck camper because the wife has bad knees and was having trouble with over cab bunk. We loved the truck camper for the same reason we bought a B it could be parked almost anywhere. If you're not afraid of an older B you can find one in your price range. Newer you will need more money.