The seat height of wheelchairs are 19 inches, electric mobile carts are a little higher, about 20 inches. A standard chair is 19 inches. Or in a nutshell no different in the window height. The door, better make it 36' but 42 would be better.
My wheelchair is 22 inches,but I'm big,yes 42" doorway is much better than 36" ,I don't always hit the doorway straight on. Add a few pictures if possible,I'm always looking for a different mouse trap.