Hi mjgh06,
There is more about the different types and blends of latex in post #6 here. Like all latex … synthetic latex is a very durable material (it would be more durable than the polyfoam layers in your mattress for example) and with only 1/2" of lower quality/density materials in the mattress (the 3 lb memory foam) there would be no “weak links” in your “revised” specs 
Phoenix