Hi Nevermore,
The durability of a mattress will depend on the type and quality of the materials that are used inside it much more than the name of the manufacturer on the label so you would need to know the specifics of a mattress to be able to assess it’s quality/durability and make meaningful comparisons with other mattresses.
There is more about the factors that can affect durability and the useful life of a mattress relative to each person in post #4 here and the posts it links to.
There is also more about the many factors that can affect the sleeping temperature of a mattress in post #2 here.
Quality Sleep and My Green Mattress are very knowledgeable about all the materials in their mattresses and will give you good information about all the materials in their mattresses and help you assess their relative durability and sleeping temperature. They use high quality materials relative to the budget range in all of their mattresses and as you probably know they are members of this site which means I believe they compete well with the best in the industry in terms of their quality, value, and service.
I also wouldn’t pay much attention to mattress reviews (good or bad) as a way to assess the durability of a mattress (see post #13 here) and knowing the quality/durability of the materials in a mattress will be a far more effective way to assess how durable a mattress is likely to be.
Phoenix