For comfort I use at 1" of closed cell neoprene foam with gel pad insert. I start out with at least 1/2" on the bottom. Then I take another layer of 1/2" and cut out a hole to near exact dimensions of the gel pad I am inserting. I make sure that there is at least 1" of neoprene at the perimeter of the gel pad for support. Then I glue the neoprene sheets together, with 3M super 77, making sure the hole is centered. Then stick in the gel pad making sure that glue is in contact where the gel pad meets the neoprene. After shaping the foam I cover the whole thing with with another layer of 1/8" neoprene to seal it all in, and hide any undesirable seam exposures. After about 300-500 miles the seat will be broke in nicely and will be conformed to your non existing butt. I hope this helps ya out. It sure did help my butt, and my customers who ride rigids say the same.
Steve