After 20 years with car and small trailer, then a few years with car and tent, I have happily gone solo in a small (fits in one parking space) class C for over 30 years. Plenty of space for one person and the bathroom is right there.
Questions to ask yourself before buying a B or small C:
If the toilet is the more commonly offered cassette type we are seeing now, can you handle this? My aging back is quite happy with a black tank that requires moving only a lightweight hose to dump it. Pulling a full cassette out of a camper is not possible for me. Even if you can handle this weight now, how about a few years from now?
Where are you going to keep this vehicle when not using it? Are you allowed to have it at your main residence? Storage lots are expensive. Plus, the car/RV shuttle to/from such lots can be a major pain for a solo person.
Maybe try out your vehicle of choice by renting before committing to buying one.
Happy travels!