Hi slidergirl,
Thanks for your reply! I'll read the threads on seat cushions as you've suggested. Those "popular choices" you wrote about are the EXACT ones I've been seeing and reading about on the internet. They call claim to be "the best" and the "most comfortable", but who can tell without trying it out personally, you know?
Please let me know how much you like/dislike the REI seat cushion you have. I like the fact that it's self-inflating and folds up for easy packing. Thanks for posting!