I recently struggled with the same thing on my BN6. I put on new foam cushions and new wooden seat bottom frames. It looked great, but felt like I was sitting on a chair rather than nestled snugly into the car like my old worn out seat. I started out removing a bunch of foam. Instead of just making it shorter, I kept the original height and removed a bunch of cylindrical cores out of the solid foam replacement cushion (using a ~1.5" hole saw, just the bit, not a drill) until it looked more like the waffle pattern of the original. I also used a jigsaw to cut out the bottom of the seat frame, basically to the edge of the metal frame, which allowed the cushion and my butt to drop down all the way to the carpet. Instead of going with the smaller diameter steering wheel, I decided to remove the angled portion of the wood frame that supports the front edge of the cushion. This may seem a bit drastic, but it lets my thighs drop down a couple inches. To me the position is more secure as my right thigh now gets a good bit of lateral support from the transmission tunnel.
Anyway, seats are subjective, and being comfortable trumps originality in a driver (IMO). Good luck