instead of sleeping * on * a pad which has a flat surface, and your shoulders and hips have their pressure points... how about something completely different.
assuming you are a back sleeper:
take a tight T-shirt that fits you, overlay it on a sacrificial foam pad, follow the outline and make a cut-out of it. somehow attach that 2-dimensional foam cut-out of a T-shirt to your sleeping shirt, use velcro, buttons, sewing or clips.
make the bottom of the shirt cut-out a bit longer, to cover the lower back.
when you lay down on down back, you are only using just enough foam padding for your back, and none of the extra mattress space.
then all you need after that is a pillow, which as discussed in other posts can be a variety of clothes in a stuff sacs or air bag containers.
I'm thinking a shorty sleeping pad the size of a T-shirt is really all we need. why have a mattress that covers unused areas. It will look like back body armor. the advantage is that it you will not roll off the pad, it will serve as insulation, you can wear it INSIDE your sleeping bag, especially if you get those backless Big Agnes sleeping bags.
just a thought.