Hi damonmcm70,
I’m sorry to hear that your Nest Bedding mattress isn’t working out for you as well as you had hoped. As you say it is sagging (all foams will take a bit of a set over time), it is an actual impression that is over the 1" warranty guidelines of Nest Bedding, or is it just a softening in the area, which I term a “phantom” or “virtual” body impression?
Also, what are you using for both a frame and support system under your mattress? Whenever someone comments about a mattress having a sag, I always suggest a “ground up” assessment to make sure that there is nothing under the mattress that may be contributing to a premature sag within the mattress.
It wouldn’t be a particular brand that you’d be looking for, but specific componentry within a mattress that you’d want to look for. Post #2 here has some information about the gradual softening of all foam that may be useful for you to manage your expectations.
Post #3 here has some good information about all foams and how they rank generally in durability. Latex will tend to be your most durable foam, followed by higher density memory foams and then higher density polyfoams.
Phoenix