I used the standard vans comfort-foam and had Abby at Flight-line interiors do the fabric work.
I had a Hangar neighbor who used those high back bucket seats and it looked awkward to get in and out. Plus, he didn’t bolt them in he only hoisted it in when he flew and he and the seat belt kept them in place when flying
Remember, when you get into the RV8, it seems easier to step in on the seat, sit down on the top of the seat/roll bar and then slide down into position.
I don’t see that happening with those tall buckets.
Unless you are planning on a lot of knife edge flight, you don’t need that lateral support.
And, as stated above, it is handy to sit in the front seat back/brace when getting in, so I don’t care for headrests or a rollbar for standard canopies.