Gosh, that's rough. Pretty much all of us over 60 have some sort of medical issues we have to deal with when on the road. Hopefully you can get some meds to help out, and work out a way to get them when on the road.
Geez, you can hardly get to Montrose without going over an 11,000' pass. And Santa Fe is 7,000' too. If you are leaving Houston permanently, you could possibly relocate to a somewhat higher, inbetween elevation and your blood oxygenation will adapt over time, which sounds like something useful.
I bought a Savana 2500 van 3 years ago, so basically identical to your Chevy. I did a very minimalist build, so it's really sort of a metal tent. I live in S&B, and have been traveling about 1/3 of the time (before covid). A lot of stuff you can work on and refine over time. Your ideas will evolve as you go along. Good luck.