If Steven cannot sleep comfortably on a self-inflating Thermarest of that vintage, I think it is very unlikely he would sleep any better on a Ridgerest.

There are a variety of options that would give him 2.5 inches of padding underneath. There are the Big Agnes air mattresses (both insulated and non-insulated). There's the new NeoAir from Thermarest. There are several brands of DAMs (down-filled air mattresses), which are very pricey, but comfortable.

The main thing about choosing air matresses is knowing what the ground and air temps will be at night. An uninsulated air mattress tends to get pretty cold under you at temps that drop into the 40s. Cold people don't sleep well, as a rule. In summer, at lower elevations, this is not a problem.