You could use a number of garments from flannel PJs to a manufacturers specifically designed product.
You need to vary the undergarment due to water temperature variations. For the warmest dry dives I use basic champion sweats. Anything warmer and I dive wet. (55F and above) Next stage I add a set of polypropolene long underwear. Then I switch to a hollis AUG 100 undergarment and if that isn’t enough alone I’ll add the poly underwear with it. I also use thermotec socks with the drysuit.