Hi jadespider,
The Eight Sleep mattress has been mentioned previously here on the forum. You can read more about it in post #44 here. They’ve expanded their lineup since that last post.
Your specifications are just a bit incorrect. The top layer is one of the new breed of what I term " high performance" polyfoams , and it is 2" of 12 ILD 3 lb density. They list is as “latex-like” on their web site, but it is polyfoam. Beneath that is 2" of 11 ILD 4 lb memory foam. Under this is a 2" piece of 22 ILD 1.8 lb poly foam and then a 4" piece of 35 ILD 1.8 lb polyfoam (these two layers are not memory foam as you had listed). These would be good quality materials for most, but I would provide a caution for someone in the “above 200 pounds or so range” with the 1.8 lb support core and the 4 lb memory foam. I’m not quite sure what you’re referencing regarding a BMI score of 250.
When choosing between latex and memory foam, like so many things, it can come down to simple personal preferences. Latex has an unusual combination of surface softness and deeper firmness/support that comes from its elasticity, it’s point elasticity (ability to conform to the shape of a body) and its compression modulus (the ability to get firmer faster with deeper compression than other types of foam). This means that it can enhance the pressure relieving layers above it because of its surface softness and point elasticity but it is also very supportive and can “stop” the heavier parts of the body from sinking in too deeply. It is also very resilient (it returns a high percentage of the energy of compression instead of absorbing it like memory foam which has very low resilience) so it can enhance the “feel” of the mattress by making it more responsive and more adaptable to different body profiles and sleeping positions rather than the less responsive feeling of memory foam or the stiffer and less adaptable characteristics of polyfoam. Latex is also a very durable material (it’s the most durable of all the foam types) so it can add to the durability of a mattress compared to other materials but the deeper layers of a mattress have less effect on mattress durability (a mattress will soften and break down from the top down) and more of an effect on performance and support/alignment so this would be less of a factor in its use. Some people prefer the more “buoyant” feel of latex, while others prefer the motion-deadening feel of memory foam. Regardless of what you choose, make sure you find out the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
Phoenix