Hi ZRock,
I did some additional research in the Sioux Falls area and added a couple of retailers to the list in post #3 here.
The 4 manufacturers and retailers that are now in post #2 and #3 would certainly be where I would focus my efforts. both of the two retailers I listed carry gel memory foam and/or other memory foam mattresses.
With your higher weight it becomes particularly important to make sure that the comfort layers of your mattress use high quality materials and that the support layers are firm enough to provide good support. What will work for more “average” weights is not likely to work well for you and your higher weight will lead to more rapid foam softening so foam quality and durability is particularly important in your choices.
I would also consider latex because it is generally more durable than memory foam and it can be just as pressure relieving as memory foam in the right combination although it is a fast response material so it will feel differently. It is also more breathable than other types of foam and sometimes with heavier weights you will sink into the mattress more and this can lead to increased sleeping temperatures because you have more insulating layers around you.
The type of ticking (cover) and quilting layers in the mattress as well as the mattress protector and sheets and bedding you use can also have a significant effect on sleeping temperature and in general more natural and breathable fibers work better than synthetic fibers and materials.
There is more about the many factors that help with temperature regulation in post #2 here.
Some of the best online and “on the phone” sources and manufacturers are listed in post #21 here. All of these are members of this site and I think highly of both their quality/value and their experience and knowledge about their mattresses which can help their customers make the most suitable choices for their needs and preferences.
The low end Optimum have a low density base layer which IMO would not be appropriate for your weight. Their gel memory foam is also under 4 lbs. Regardless of whether you purchase locally or online though … I think it’s always a good idea to test some mattresses locally to get a clearer sense of the types of mattresses that work best for you and you have 4 better choices available to you and these would be where i would focus my attention. I would also avoid major brands either as a purchase option or even as a “target” that you hope to match.
The difficulty with even testing a major brand is if you happen to like one of their mattresses … you would need to match the “feel” by testing another mattress with better quality and value anyway because they don’t disclose enough information about their mattresses to even come close to matching them based on specs. The difficulty with this is that matching one mattress to another based on how they feel to you is not very accurate unless they are both side by side in the same store and you can test one immediately after another (our memory for subjective “feel” doesn’t last very long and isn’t very accurate). Because of this you may as well only test mattresses that have better value right from the start. There is more in post #2 here (and the links to other posts it includes) about “matching” mattresses and the difficulties of using a specific mattress as a “target” instead of a more specific and objective set of criteria.
Phoenix