When they don't leak or have holes the old Vietnam-era GI air mattress (the "Rubber Bitch") was pretty comfortable (especially if you have hip issues). I still have mine.

When you eventually develop a leak or hole you'll have to hold the inflated mattress down in your bathtub to find the bubbles, dry, then patch with Shoe Goo or Gore-Tex waders glue and a patch

The grey GI Ensolite closed-cell roll-up pad replaced them because they weren't / aren't especially durable. The brown Marine folding accordion pad stores better but isn't any more comfortable.

For me the Thermarest pad is just OK. A cot is nicer, but not if you're dismounted and packing it in your ruck.