Ted,
For my -8, I bought a box of tempur foam from Jim and Janice Fix at Hi Tech Foams
http://www.seatfoam.com. This kit contained all the foam I needed for many layers of custom fitted backs and bottoms as well as armrests and headrests. I glued and sculpted them to my wife and my bodies. Buying the kit allowed me to use three densities of Nasa foam: hi for the bottom layer, med for the middle layer and lo density for the layer closest to the skin. (Oregon Aero uses only one layer of tempur foam, I think, I could be wrong there). Glued them to alum plates and handed them over to a local hot rod upholsterer.
Oh, I also found an FAA burn approved snythetic leather called Ultra leather
http://tapiscorp.com/index.html. Feels butter soft, easy to sew, relative to leather, certified FAA burn tests, and is breathable, so it's comfortable. A little more work on my part, but my seats are custom to me, and they fit my body perfectly. The best part is my wife's seat: she now hates the 'store bought' seat in our old Mooney and cannot wait to fly in the Rv. It's the man/machine interface and to me is the most important thing to spend a little extra time/cash on. BTW, total cost for the whole thing was around $600.
Art