Hi lxjenkins,
The Ecosleep is a good value in a mid range mattress using 4 lb memory foam and a 2.0 lb (good quality) base layer. You are right that 4 lb memory foam won’t last as long as higher density memory foam or latex but lower density memory foam also tends to have a more “movement friendly” and less temperature sensitive feel and is often more breathable and cooler (depending which of hundreds of types of memory foam it is) than the higher densities. All of this of course is part of the many tradeoffs between price, performance, durability, and the many different “feels” that are possible with memory foam and different types of laering.
Some other online memory foam choices with good value and various other layering options are in post #12 here.
The choice between latex and memory foam is a personal preference issue and they are very different in how they feel and perform as well of course in durability. The Queen adjustable Ultra Plush is also excellent value but whether it “fits” with the type of mattress you are looking for really depends on how you feel about the two very different materials. Memory foam is a more “in the mattress” type of material (to different degrees with different types of memory foam) while latex is a more “on the mattress” type of material. You can read more about the pros and cons of memory foam here and latex here but how you feel about actually trying out or sleeping on each material is just as important a part of choosing between them. There are some people who even prefer a combination of both but this would also increase the price of the mattress (latex is more expensive than memory foam).
So overall the two choices you mentioned are both good ones with great value IMO … but the decision between them would be based on your preferences and the qualities of each material that are important to you (your own “value equation”) rather than one being a “better” choice than the other.
Phoenix