Hi southernbelle91,
The first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choices … and know how and why to avoid the worst ones.
I would also read post #3 here which has some suggestions for people that are in higher weight ranges. As you can see I would make sure that any mattress you are considering uses higher quality and more durable memory foam and polyfoam and I would minimize the amount of memory foam that was under 5 lb density.
You can read more about the different types of support systems that generally work best for different types of mattresses in the foundation post here. Most foam mattresses (such as polyfoam, memory foam, or latex foam) generally do best with a firm non flexing support surface that provides a large contact area and even support across the surface of the mattress and allows most of the flex in the mattress to come from the top layers. These would generally include a rigid foundation on a steel or wooden bedframe or a platform bedframe with wooden slats or a wire grid support surface that has minimal flex such as the one you are looking at. You can read a little more about the types of wire grid platforms you are considering in post #10 here and while it would be strong enough to hold you … I would tend towards one of the versions that has more longitudinal wires and a more supportive surface with less “gaps” in between the wires that would reduce the risk of the mattress sagging into the gaps in between the wires over time.
A box spring on the other hand has springs inside it that flex which are an active part of the “sleeping system” and can change the feel and performance of the mattress in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) … especially with higher weight ranges that will compress the springs more. They can also have an effect on increasing motion transfer. They are much less commonly used for foam mattresses because foam doesn’t need the shock absorbing ability of a box spring. While they can provide an evenly supportive surface … if you test a mattress on an “active” support surface and it is a good match for you in terms of PPP then I would keep in mind that if you use a different support surface under your mattress that has more or less flex than what you tested it on in the store that it can change how the mattress feels and I would try and test it on one of their adjustable foundations in the flat position so that you can see what it feels like on a support system that has no flex (see post #2 here).
The tutorial post also includes a link to a list of the better online memory foam options I’m aware of and if you let me know your city or zip code I’d also be happy to let you know about any of the better options or possibilities I’m aware of in your area.
Phoenix