Hi sunshine,
You are the second one on the forum who has mentioned the Green Choice at Denver Mattress so I thought it was time to find out a bit more about them for the benefit of others who may want to know about them.
I called a few outlets and they are apparently only available at a limited number of Denver mattress outlets and there are no current plans to add them to the website.
I didn’t get the specs of each of the 6 or so different models (each of which have a different layering and feel) but in general terms they are imported from China and use various combinations of 3 lb density memory foam along with various layers of polyfoam in the comfort layers and the support core. They weren’t able to tell me if any of the foams used were certified for offgassing through CertiPur or another testing method so for those who are concerned about any offgassing I would take this into account.
Post #6 here also has some information about the additional uncertainty that can be involved if you are buying a mattress that is made in China.
They told me that a reasonable expectation would be that a customer would need to replace them in about 3 or 4 years although of course this would depend on height and weight and sleeping style along with the frequency of use.
These would generally make a more suitable choice for a child (if they were old enough that any memory foam mattress was suitable in terms of offgassing and support/alignment) or someone who was very light because of the low density/durability of the foams used. They also told me that they used more temperature sensitive memory foam and would tend to be on the “warmer” side of the spectrum for memory foam mattresses.
So overall … these would make a good choice for those who were either very light and/or were looking for a lower quality/price memory foam mattress for a spare bedroom or who didn’t mind that it wouldn’t last as long as a higher quality or price choice.
Thanks for mentioning them and motivating me to find out more about them 
Phoenix