If you want a lower seat, just peel back the front cover (remove staples first), remove all the padding in front except for first six inches, put cover back in place. Then, place
AirHawk R cushion on top. You'll get a 2" lower than OEM seat, and it's more comfortable than any other combination I tried. And I tried several dozen, including gel or all kinds.
If you don't need a lower seat, put the AirHawk R on top. If you need a little lower, just remove half the padding after the first six inches.
Using the AirHawk R is the most cost-effective option I found, for comfort and height.