SMB with shower!
For some reason it is popular on this site to bash the Sportsmobile brand and to look down on inside showers. We had Sportsmobile convert our high roof 144 Sprinter 4x4 a couple of years ago and the quality is excellent. Our previous rig, an Alaskan truck camper was nice, but having an indoor shower enclosure with a private cassette toilet is a really nice luxury in the back country. I’d keep those items on your must have list.
Regarding the third captains chair, do I assume correctly that a forward facing rear couch bed with seat belts wouldn’t suffice for your third person? If that would work, you could probably get everything you need in a 144 Sprinter.