Hi mister,
Typically side sleepers need thicker/softer comfort layers than other sleeping positions and heavier weights also need thicker but firmer comfort layers to relieve pressure. In addition to this … with heavier weights it is especially important to use the highest possible quality materials in the upper layers of a mattress because they will soften and degrade much more quickly than average.
Support on the other hand comes primarily from the firmness of the deeper support layers in combination with the thickness of the comfort layers (how far the heavier parts of your body are allowed to “travel” before they are stopped by the firmer support layers).
You can see the partial specs of the construction of your mattress here.
As you can see it has 3.5" of foam in the comfort layers (2.5" of memory foam and 1" of polyfoam) which may be suitable for your needs in terms of thickness but the problem is that all of the materials are probably too soft which means that you would go through them more and require the “help” of the layers below them (in this case the innerspring) for pressure relief. In this case … your support core is the softer innerspring (higher gauge) which would assist the pressure relieving layers more but for your weight would compromise alignment. In addition to this … the comfort layers also use low quality/density materials which will soften more quickly than if you used firmer higher quality materials in your mattress.
Combination stomach/side sleepers also need the thinnest/firmest possible comfort layers which “just barely” meets your pressure relief needs and the a firm support core to prevent the alignment issues that come from sleeping in a swayback position on your stomach. As you know this mattress is not a good choice for your body weight and sleeping style and your experience of alignment issues would be “expected” on this type of mattress in combination with your body type and sleeping style.
So what you have is a mattress that overall is probably soft enough in the upper layers for pressure relief but too much of the softness comes from the support system so it is compromising your alignment. You would probably do better with firmer comfort layers (which will be softer for your higher weight than they would be for a lower weight and better for stomach sleeping) and then a firmer support system underneath this to provide better alignment (in all your sleeping positions). The firmer foams on top would lessen the amount you would sink in and go through them and then the firmer support core would help “stop” your pelvis hips from sinking in too far. You would also need higher quality more durable materials in your mattress (avoiding low quality/density polyfoam and memory foam as much as possible) to have a reasonable expectation of durability with your higher weight. Even if the mattress was “perfect” for you … the softer foam will soften further much too quickly. If you did choose a Simmons (which I wouldn’t anyway) … then their firmer lower gauge innerspring would be a more suitable choice.
In looking at what is offered by Mattresses Unlimited … there seems to be very few good choices available to you. You are in a very similar position to the poster here from yesterday and to the forum members in post #66 here and the other posts it links to.
These posts will give you some good suggestions about what may be possible when you are “between a rock and a hard place”. Unfortunately there are very few good options that I can see at Mattresses Unlimited.
Nashville Bedding (AKA Southerland): is their low cost promotional line.
Simmons: If you were to choose one of these I would make sure it was the firmest of the pocket coils (and pocket coils may not be the best choice anyway for your weight) and the least possible amount of foam on top and then use a topper to create your own comfort layer. These types of mattresses would be labelled “extra firm”.
Enso: These are memory foam mattresses that use lower density memory foam which would not be suitable for your weight. They also have listed prices that are much higher than other retailers that sell these same mattresses.
Sealy and Stearns & Foster: You mentioned that they carry these and there may be some options here (in terms of extra firm mattresses that use much thinner layers of lower quality foam in the comfort layers and would be suitable for a topper) but their website doesn’t mention them so I don’t know what they carry.
Tempurpedic: While the best of these are good quality … they are also not great value and much more expensive than other memory foam mattresses that use similar quality materials so you may be trading up in price. If you choose one of these I would make sure you avoid any of the lineup which uses less than 5 lb memory foams (avoiding the Cloud line for example which uses 4 lb memory foam) because again they will not last long with your weight.
Southerland: These have some possibilities in their mattresses that use latex layers in various thicknesses over polyfoam. Unfortunately they are also priced at much higher prices than they should be IMO (and higher than other retailers that sell them). Perhaps their prices are just “starting points” for negotiation. These may be good choices (assuming that the one you choose has the construction that best matches your needs and preferences) because at least they use high quality materials in the upper layers of the mattress. if you do go in this direction I would make sure that you choose the firmest comfort and support layers possible and test the mattress carefully in the store for alignment (along the lines of post #11 here) because they don’t list the details of the firmness of the layering and also don’t list the density (quality) of the polyfoam layers underneath the latex.
If you know the details of the Sealy and/or Stearns & Foster mattresses they sell then there may be some possibilities there as well that are “less bad” than some of the other choices that they have available. The firmest of the Stearns & Foster luxury latex (with the least amount of polyfoam) may be a good base for a high quality topper.
Phoenix