I run with BeadRider beaded cover. They are motorcycle specific.
http://www.beadrider.com/
As to the OP: I ran a sheared sheepskin over a stock seat for awhile. The sheepskin I used was from a WalMart car seat cover. Didn't help my marshmallow butt. I then switched to BeadRider beads with a stock seat. Good improvement, although I found that my butt would roll forward when braking. I went to a RoadSofa seat without the BeadRider for a while, but I soon added the BeadRider to RoadSofa. In the summer heat, I found the RoadSofa very hot, perhaps because of the gel insert. Adding the BeadRider to the RoadSofa made for the most comfort.
Perhaps, instead of putting the sheepskin over the beads, try putting the beads on top of the sheepskin.