Hi Alleson,
You are in a kind of āisolatedā location and the only independent mattress manufacturer I know of near you is ā¦
Harness Mattress who is a local independent factory direct manufacturer in Harrison
There is also an outlet that carryās Savvy Rest mattresses here ā¦
Mountain Organic Bed
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These are a āchoose your own layersā latex mattress that can be customized for each individual person. While they are too expensive IMO ⦠they would give you a very good idea of a suitable layering in latex that could work well for you. You could then duplicate this mattress through an online manufacturer (such as several on this site) at a substantial savings.
In terms of memory foam ⦠the night therapy is a Zinus brand so it is Certi-Pur certified but there is no information about the density (quality) of the memory foam. It is likely 4 lb or less (medium quality) as this would be typical for a Zinus brand and this price range. I would personally not consider any memory foam where the density of the memory foam was not known as this is a key part of its quality and feel. If you are looking to purchase memory foam online from an outlet such as Sams club (so you can always return it at no cost) then I would look at the Aerus 4 lb memory foam mattresses. Aerus is made by Foamex and is the most breathable of the good quality memory foams IMO. I would avoid all memory foams that are under 4 lbs.
The feel of memory foam mattresses can be very different depending on the thickness and density of the memory foam, the manufacturer of the foam, and the type of polyfoam layers underneath it which is the āsupportiveā part of the mattress (memory foam is a non supportive foam and needs a supportive foam underneath it). What is suitable for one may be completely unsuitable for another depending on weight, body shape, sleeping positions, and preferences.
All memory foam would be considered āsoftā although many are much firmer when they are cold and there are wide differences in how each type reacts to heat, humidity, and pressure. Buying memory foam online without a fairly clear idea of the type of memory foam and polyfoam layering that would be suitable for your own unique needs can be very risky ⦠especially without a good return policy.
As you probably know from this thread ⦠the Serta iComfort IMO is poor value as are almost all of the mattresses from the major manufacturers (the āSā brands) including Tempurpedic. While there are many memory foam mattresses that are better value and similar or even better quality to Tempurpedic ⦠it is important to know how to make meaningful comparisons.
The best way to purchase a mattress is to focus on what is in them rather than on brand. If you know the difference between memory foam, latex, and polyfoam (the one to avoid) in the comfort layers and you know the difference between polyfoam, innersprings, and latex in the support layers, and you have a good idea of how thick and soft your comfort layer should be (depends on your weight and body shape and your sleeping positions) then you will be in much better shape to know the type of mattress that would work for you.
The prodigy has an inch of latex (slow recovery latex) on top so is slightly firmer than the revolution because the latex would reduce the tendency of the memory foam to soften with body heat. Overall though ⦠this comfort layer would be far too thick for almost everyone and would be risking misalignment in the spine.
The cloud luxe is also very soft but at least has only 4.75" of memory foam on top (which is still too much for almost anyone). The cloud series would also be much more suitable for people who were a lighter weight.
Once you have a good idea of the two basic functions of a mattress and the different materials and layers used in the comfort layers and the support layers and how your sleeping positions can make a big difference in how thick your comfort layer should be, you will be in a much better position to test mattresses and make decisions that donāt depend on the āstoriesā that so many sales representatives will try to tell you. Most of these are designed to get you to purchase ātheirā favorite mattress rather than the best one for you.
A topper can certainly help a mattress that is too firm ⦠but if you already have 3-4" of memory foam (or other soft foam) on top of a mattress (all memory foam is soft as it becomes warmer) ⦠then a topper would be unlikely to do anything but put your back out of alignment over the course of the night as it would make your comfort layers much too thick. Toppers are much better at āfixingā a mattress that is too firm and has thinner comfort layers. It is very difficult to āfixā a mattress where the comfort layers are already too thick or soft.
Hope this helps and feel free to keep the questions coming 
Phoenix