Sorry that you are not liking your S 250. I have 5 bulging disc in my lower back but the S 250 seat does not hurt me when I ride it. And I ride it almost every day.
The problem I have with it is it does not fit my butt just right. I was going to take the cover off and scoop out about 1/2 inch of the foam.
Since you reported that the seat material is glued to the foam I guess I need to rethink that. I can live with it the way it is, I just wanted to improve it a little.
Hope it works out for you.