I fixed the problem of the squishy foam used by the manufacturer. I took the foam from one of the cushion bottoms down to the local foam store. I asked for and got the best foam they had, and had them cut two to fix the cover.
Made such a huge difference. Unfortunately, the sofa foam is another story. It's a much more complicated foam cut, and haven't tackled it yet.
Back to the dinette for a moment. I left the original foam in the back rest cushions. They are fine with no more pressure than they get.