Lowering the seat foam

I want to replace my seat foam, because the foam rinse to the carpet. I like to sit low in the car and in the seat. With a new foam, i sit to high and the feeling is like to sit on a big ball.
I want to lower the middle section and need a tip. Should i shave it in the middle and put in a softer foam ( to keep the vinyl tight ), or should i shave the foam on the spring side?

Thanks for your help
Marco
On the stock seats you can lower them a half inch (?) removing the 4 spacers on the mounts. Removing foam padding may be uncomfortable and leave wrinkles unless you can stretch the cover. If you look at the springs you will see how they are tentioned front and rear by a bend in them, you may be able to unbend them alittle to get some sagging effects.