Hi crazydiamond,
I’m not sure which model you chose but besides the lower quality/durability of the type of gel memory foam they use and the low density of the Comfortlast support core (which is apparently only 1.5 lb density) … all of the models except the Insight includes polyfoam in the mix of the comfort layers. Some of these are “omitted” in the layer descriptions on the Serta website. These vary from 1" - 2" of either “support foam” or “comfort foam” in the different models. While an inch of low density polyfoam in the upper layers by itself may not be a big issue if it was the only “weak link” of the mattress … in combination with other less durable materials it may contribute to softening and loss of comfort or support over time and be one additional factor that reduces the useable lifetime of the mattress.
The latex used in mattresses is not generally a material that affects people with latex allergies unless they are the more serious Type 1 allergy which like all allergies which can induce anaphylactic shock (like a bee sting for some people) can be very serious indeed. Post #2 here has more information about latex allergies and how unusual it would be for latex foam … even for those who are allergic to other rubber products like gloves or condoms.
Phoenix