Hi kbalz,
You are down to two choices which are among the best of the best value in the country and once you have eliminated the “worst” choices … the differences between your final choices wouldn’t be about “best or worst” any more but about which one of the objective, subjective, and intangible differences between each mattress and merchant best fits your personal “value equation” (see post #46 here) and which of the tradeoffs involved in each are most important to you.
You are also comparing apples to oranges because one is all latex and the other is a polyfoam/latex hybrid and you can see some of my thoughts about pros and cons of each type in post #2 here.
As far as a foundation goes … it would depend on which mattress you chose. If you choose an all latex mattress … then a foundation that has more closely spaced slats (3" or less apart is preferred) or a closely spaced wire grid with a good cover and if you have a polyfoam base layer then the more closely spaced slats or wire grid is not quite as important (polyfoam is less flexible and elastic than latex and doesn’t sink into the gaps as easily)
The foundation thread here will give you much more information about the many foundation options available and which would be most suitable for different types of mattresses and different preferences if the manufacturer doesn’t sell one or recommend one to go with the mattress.
Phoenix