Don:
I am in the process of measuring seats to find one that will fit my truck. I have become spoiled to a middle armrest and am looking for a bench seat with one that is the correct width.
My father-in-law is in the boat upholstery business and from what I have witnessed over the years is how much a foam sheet will improve the firmness of a spring seat. I would believe an inch and a half of high density foam would correct the softness of your seat. You would, however need to rip out those pretty seams to install it.
