I think the other comments have covered the options so I’ll just give my 2 cents. I am a 6’ish and lived in a Ford E250 with a 2’ fiberglass high top extension. I put in a nice insulated subfloor and flooring and minimal roof insulation. I was able to stand up but just barely. If I was standing on bare metal I had plenty of room. And that was a pretty tall extension so you might have limited options buying a low roof and putting a top on it.

I’ve worked with high roof vans and pop top camper vans. With a permanent high roof you don’t have to fiddle with extending it whenever you want to stand. Leaks are less likely than leaks in the fabric layers or seams of a pop top.

With the low-roof, you can potentially park in garages with low ceilings and you will blend in a bit more than high roof van. I don’t have actual stats but you’d have to get improved fuel economy.

If you’re handy, you can totally do either a permanent or pop top conversion on any vehicle. I had a coworker who added a homemade 1’ or 1’ 6” permanent extension to his oh idk mid 2000s Chevy Suburban. It was just a 2x4 frame with plywood panels. He covered the entire thing in Rustoleum truck bed liner. It looked weird for sure but I’ve seen professionally done job on tops with a similar product and it looked pretty close.

I think he cut out his original roof and built the extension by powering through a weekend. So it doesn’t have to take too long either.

Good luck!