Hi DH333,
Some of the information in post #2 here may help you decide on the type of materials you are comfortable including in your mattress in terms of “safety” and VOC’s.
In very general terms … memory foam is the “best” for motion isolation but latex and pocket coils are also very good at isolating motion between couples as well (see post #18 here). Support cores that use innersprings that are joined together with helical wires (not pocket coils) will generally transfer more motion than other types of materials and components.
There is also more about the pros and cons of memory foam vs latex in post #6 here.
Latex is the most durable of all the foam materials and it will soften and sag less than any other type of foam regardless of which manufacturer uses it in their mattresses. There is more about the variables that can affect the durability and useful life of a mattress relative to each person in post #4 here.
The Dreamfoam Ultimate Dreams has a much lower percentage of people that experience sagging than you would normally find in a mattress in this budget range or that uses lower quality materials but there are some comments in post #2 here that will put some of the comments about sagging into better perspective.
There are too many unknowns, variables, and personal preferences involved for anyone to be able to predict whether any specific mattress will be a good match for someone else in terms of PPP based on specs (either yours or a mattress) or “theory at a distance” and when you can’t test a specific mattress in person … then the the best source of guidance is always a more detailed conversation with a knowledgeable and experienced online manufacturer or retailer who will know more about their own mattresses and how well they are likely to “match” different body types and sleeping positions based on the “averages” of their customers than anyone else and can help “talk you through” the options they have available that would have the best chance of success (see mattress firmness/comfort levels in post #2 here).
There is also more in post #13 here about the most important parts of the “value” of a mattress purchase that can help you make more meaningful comparisons between mattresses.
Phoenix