Hi wheezer,
Everything is relative to each person’s personal experience and circumstances but there is some generic information in the “putting the layers together” and in the “sleeping style, preferences, and statistics” sections of the site as well as the tips and tricks page here.
So as you can see while heavier people do tend to do better with firmer layers … don’t forget that your goal is PPP (Pressure relief, Posture and alignment, and Personal preferences) not anyone else’s theories.
The suggestions I have for foundations (and that also includes some platform beds that would be very suitable for an all latex mattress) are in the foundation thread here. The issue of beds (except for the occasional comment from members here or links which are posted along the way) is outside of the scope of a forum dedicated to mattresses although I certainly welcome any discoveries you may find 
Phoenix