Hi there,
When it comes to motor trimming, i'm no expert, but i can pass on some basic info that may be of help to you.
I recently replaced the original two front seats upholstery in my '73 convertible. The vinyl and the foam padding were all factory original in good all 'round condition except for one small spot where the stitching had let go through age. After a few attempts to repair the damaged stitching problem, over a four year period, sadly the vinyl had to end up being replaced. I am very fortunate to have a first class motor trimmer in my city who looks after all my trimming needs very well.
I talked over the front seat upgrade with him and we discussed what we were going to do about the original foam - keep it or replace it. I told him that i could get hold of Mustang aftermarket seat replacement foam from several companies in America to upgrade the seats, but he said no to that, as his vast experience of replacing classic car seat foam, had led him to custom make his own foam inserts for a better fit and offer better padding. He explained to me that when it comes to car seat foams, there are a wide range of quality foams out there, and a variety of different densities of foam material available to offer different levels of comfort and support. He guided me in helping to select a foam that would offer good backside support as well as good lumbar support.
He also custom shapes and cuts the foam to deliver a good fit up and put the support where it's needed the most.
This has made a world of difference to the comfort level my new seats now offers up to me. I can now drive around for hours and not feel uncomfortable in any way. Wow! what a difference it has made. So in your own case, going down a similar road as i did, should also make a world of difference for you too.
Try and find a top class trimmer and discuss getting your front seats foam custom made.
Greg