Hi kmk5dc,
The first place I would start with any search for a new mattress is post #1 here. This will provide you with the information, steps, and guidelines you need to make the best choices and perhaps most importantly eliminate the worst ones (such as both of the mattresses you are considering). You can read a bit more about the Green Choice here and as you will read I would avoid all major brands or any mattress where you aren’t able to find out the quality of the materials inside it.
A quick scan in your area didn’t show many good options for buying a mattress outside of Denver Mattress in Bismark. They are a regional manufacturer which makes some good quality and value mattresses and are transparent about the materials they use. I would focus on the mattress they make themselves and disregard the other brands they also carry.
Other than that, there are a few other “possibilities” (out of the dozen retailers or so I looked at online) but these will take more research along the lines of this article to make sure they have the knowledge and experience to help you make good choices and most importantly are able and willing to provide you with good information about what is in their mattresses. If they can’t (or won’t) I wouldn’t consider them. I’ve also listed the brands I would focus on with each one where your odds are better of being able to find out what is in the mattress.
www.sleeponmattress.com Bismark, ND. They carry Pure Talalay Bliss and Savvy Rest latex mattresses and a range of Restonic mattresses as well. They also understand the importance of knowing the type and quality of the materials inside a mattress and unlike many other retailers will provide this information to their customers…
http://www.twwarehouse.net/index.html Bismark, ND. Englander
Sleepharmony in Montana, California, North Dakota, South Dakota, Minnesota, Washington, and Wyoming | Conlin's Furniture | Result Page 0 Bismark, ND. Sleep Harmony (memory foam and hybrid)
Other than this the closest options or possibilities I’m aware of would be in the Fargo, ND area and are listed in post #3 here.
Phoenix