We understand and share your trepidations with a full length bus and the "short" buses as well. We did find a bus we think is about right for us and our dogs. It is 28' bumper to bumper with 20' behind driver's seat to back wall. It drives similar to the large U-haul trucks in my opinion, a bit slower but feels the same on corners and such. I do not know about off-roading with it though. This is ours as she looked when we brought her home.
Diesel Dan's got 1 that is eerily similar to ours, he has done a great job with his and may have more insight as to living in it. His build is here:
What do you classify as a Short bus?
What are you thinking for a Mid-size?
Where are y'all at?
Maybe someone here is nearby and you can go have a look at something in RL. We found an older conversion locally that we considered buying. We opted to go to the auctions instead but we learned alot just being able to poke around a converted bus. Our daughter is the only one that has been on a bus in the recent past. For us it had been quite a few years since we were last in a school bus and we were a bit smaller back then....
So it really helped to be standing and walking in a converted bus.
Good Luck to you guys, and let us know how things turn out.