Hi TheNuke,
the choice between an all latex mattress and a latex/polyfoam hybrid would boil down to personal preference and for most people it would be a matter of budget. Post #2 here has my thoughts about both types of mattress.
A 3" comfort layer in either mattress (the primary support comes from the deeper layers) would be quite suitable for you IMO (both mattresses have a similar 3" comfort layer) but one has polyfoam in the quilting and the other has wool. My target would be the ILD’s that you believe would most closely match the feel and performance you were looking for in either mattress without a topper. It’s always an option to add a thin topper for some extra surface softness but if you do go in the direction of the Ultimate Dreams it already has 1.5" of softer quilting foam on top so I would take that into consideration and you may not even need to go in this direction.
The first step though IMO would be to choose the mattress (in either case) that is as close as possible to your needs and preferences … erring on the side of firmness if you seem to be “in between” two choices … and then after you have slept on it then you can decide if it needs anything else on top and what that should be based on actual experience rather than 'theory". I would work with one variable at a time 
Phoenix