Currently we’re looking into a lot of high-roof vans (Sprinter, Transit, Promaster).
Significant Youtube videos, forum posts, reading books, etc.
One resource I’ve found very handy is https://vandogtraveller.com/van-conversion-book-from-van-to-home/
No affiliation with them, but very in depth and engaging.
Really looked into Canadian vans, might have to start looking stateside.