You might try looking at seats for other brands. Harley has a boat load of designs, both factory and aftermarket, that might work. Seats designed for the now discontinued version of the Sportster might fit the classic better than the touring seats.
For two up seats, the Sportster Sundowner seat is pretty comfortable, all else considered. My '07 Sportster rode about the same as my '11 C5, and the Sportster did not have a sprung seat.
I attached a picture of the Sportster so you can see the sundowner seat it had. Never rode with a solo seat so cannot comment on their comfort. I put 400 mile days on the Sundowner, and while not as comfy as my Ultra, it wasn't painful.
You most likely would have to modify seat attachment points on either style though.