Hi TimJohnst,
My thoughts would be very much along the same line as Neal’s 
You can also read a little more about an all latex mattress vs a latex polyfoam hybrid in post #2 here. At the very least I would make sure that with higher weights that there are thicker layers of latex in the upper layers of a latex/polyfoam hybrid mattress and that the polyfoam was a minimum of 2 lb density to better accommodate greater weights and improve durability.
Phoenix