Good Question! I made a 2″ foam pad out of some foam I found at a surplus store. After sleeping in it for a few nights I decided it isn’t nearly comfortable enough.
I ordered one of these: https://www.amazon.com/Kamp-Rite-Queen-Self-Inflating-Pad/dp/B004M0YYEC
I think that is the same mattress that CLC used in their model trailer. I’m supposed to receive it tomorrow, so i’ll let you know how it sleeps!