I just recovered a set of seats to replace the originals in my '65.
I did it for comfort, and wow, is it a huge difference. We used what I sell...TMI brand seat foam and seat upholstery. Installed properly, it looks fantastic, and the new seat foam is really great! Original foam is over 50 years old. Even if it's in good shape, it can't compare to brand new foam.
I've been handling this brand for quite some time, and use it in all of my restorations.
I will try to post some pictures tomorrow.