Thanks, Jo for the link and explanation. I think I won't need the thermapads, DiMarie, because I'm heading south, but I think what you are describing is the type of pad I put in my shoes for warmth.
This is what I bought:
http://www.autobarn.net/gel-seat-cushion.html
A friend on the PN board with butt pain said she uses a molded gel seat, and while this isn't it, it seemed to offer the support she thought was helpful.
I don't know if we have a sticky in this forum with links to aids like this, but it would be helpful.
I can't believe I've had pain with sitting for 8 months now and nobody, not the pain doc, not the surgeon, not the physiatrists, physical therapists, neurologists. NOBODY has suggested these seats. Well, okay, I'm having a rather down day and feeling whiney, but I must say, overall, I don't feel I've had coordinated care since the surgery. The most valuable help has been from a former spine patient who used to post here, and who will answer emails with helpful thoughts. She gives me better explanations than any of my professional medical providers.
Any other aids that people find helpful in the long term management of spinal instability and buttock pain?