After too many sleepless nights from sore hips on a Z-Rest, I went to a big REI and laid down on virtually every sleeping pad they had on display, including doubled-up Z-Rests and Solites. I got a few funny looks from other customers, and ignored by REI staff – they must be used to this behavior.
I bought a small Therm-A-Rest 40th Anniversary sleeping pad, 2 inches thick, 17 ounces. I sleep much better now, because my hips hurt a lot less, and I sleep much warmer. The Z-Rest was not enough ground insulation for 40°F nights with a 30°F WM sleeping bag!
You can still find that pad at Campmor and some other retailers, but not at REI.
YMMV, but you might try your own Goldilocks test.