I hate this when it happens! I lost the link to the seat repair, maybe if you do a search. You take the seat bottom out turn it upside down, remove the wire grid that hold the stuff together. Go buy enough 2" foam and a jute back carpet sample to fit the underside of the seat. Install the foam then the carpet then put the wire grid back in. I did this to my seat about three years ago and it still feels like a new seat, Cost about $10. I hope someone saved the link to the repair and will post it.
Floyd