Hi maxwalrath,
Post #1 here has the basic information, steps, and guidelines that will answer most of your questions and help you make the best possible choices. It will also help you avoid most of the most frustrating and time wasting parts of searching for a new mattress like visiting Sleepy’s or testing major brands 
I think post #4 here about the difference between a latex/polyfoam hybrid and an all latex mattress will give you a good sense of the value of having more latex in your mattress if you can comfortably afford it. This would be particularly true with higher weights because latex is a much higher performance material in a middle transition layer. The Alexis also has more options to rearrange or exchange layers than the Bamboo Bliss which only has one latex layer.
The foundation or base is really too deep in the sleeping system to have a significant effect on heat issues which are mostly about the layers closer to the top of a mattress. You can read more about the different facctors involved in sleeping temperature in post #2 here. The advantage of having a more breathable base is more about reducing the risk of dust mites, mold, and mildew (see post #10 here) than about sleeping temperature.
The foundation thread here may be helpful.
Phoenix