i HAVE TWO SUGGESTIONS.
You could have a local upholsterer open up the stitching of the seats and insert a chunk of high-density foam to make the seat more comfortable. This will cost a few bucks, but you dont have to throw out or replace the seats...just modify them.
Personally, I found just reclining the seat a little further back meant that my spine was no longer in line with my bum so that when I hit the bumps, it wasn't so jarring to my spinal cord. You may find this reclined seating position silly, but its a no cost option.