Bench Seat Question

[Draggn66]

I've ripped apart my factory bench seat and ordered new foam. It has the zig zag springs at the bottom. Other than being broke which they are not, how do I tell if they are ok? When driving I sank down pretty far. Had to throw a pillow under me to sit right. Has anyone put a piece of plywood or something between the springs and foam to stiffen it up a bit? Or do you think new foam will take care of it? Any advice would be helpful. Thanks.....