Hi Mike,
What great questions 
In general terms … any quality independent manufacturer can use materials … including memory foam … that will certainly match the quality of tempurpedic at a lower cost. There is a list of memory foam manufacturers on the Certi-Pur site here* … most of which manufacture a range of memory foams in terms of feel, quality, and density. The highest quality memory foams of most of them (5 lbs and up) would all be high quality and comparable to Tempur material … even though they would not be exactly the same in feel or characteristics as Tempur foam. Premier for example makes 8 lb memory foams that are very dense and can be used in memory foam layers in the same way that Tempurpedic uses their 7 lb HD material. Foamex also makes higher density memory foams that are available through manufacturers or certain outlets although they are not as widely available through most online outlets. Many will even make custom density and formulation memory foams for certain outlets.
ADMIN NOTE: *Removed 404 link|Archived Footprint:certipur.us/products.html & replaced with latest CertiPUR list
For example relief mart makes memory foam mattresses that can be customized for each persons needs and can be designed in conjunction with a health professional http://www.chirosleeper.com/chirosleeper-diagram.htm
As you likely know … my favorite foam manufacturer is Foamex (FXI) because of the method they use to pour the foam (called VPF). I believe this makes a higher quality more consistent foam … but this in no way means that the other manufacturers are making poor or “lesser” quality foam. The Sensus is very high quality although in more limited supply and the Aerus is more breathable and faster recovery memory foam and also very high quality (assuming it has 5 lb density).
Essentia marketing is IMO completely misleading since as you say it is not even memory foam but “slow recovery latex” similar to NuForm made by Latex International. Vita (Radium) in Europe makes a similar material. Any manufacturer who orders from LI can use this material in their mattress for those who wish to use it although it may be a custom order. I know that several of our members such as http://www.okmattress.com/ and http://www.beloitmattress.com/mattress1.html have used it in several mattresses they have built. Even some of the major manufactures like Comfort solutions (in their Laura Ashley and King Koil), Stearns & Foster, and others use Nuform in some of their mattresses.
OMI was one of the reference points I used in testing latex mattresses when I purchased my mattress as I liked the feel of the Terra. Of course I would never pay those prices for a latex mattress and with enough testing on various mattresses, it was simple to duplicate the feel of that mattress at a much lower cost (less than half).
Part of the difficulty in “knocking off” a memory foam mattress such as Tempurpedic is that even though there are many memory foams that are similar quality … there are many variables in how each foam feels as memory foam can be formulated in many different ways with many different chemical mixtures. Each of these results in unique temperature and humidity sensitivity, breathability, recovery time, and other properties. There are also other variables such as the choices in support foam and in the ticking and quilting (or lack of it) that can make a significant difference in how a memory foam mattress performs and “matches up” to an individual or to another mattress. All of this means that it is usually wise if possible to take a trip to a local manufacturer and actually test different mattresses as this is the only 100% accurate way to know how it will feel for each individual. All memory foam mattresses only contain a minority of memory foam on top and the type and layering of the memory foam along with the choices in the rest of the mattress can dramatically alter how it feels and how it works for an individual or how it compares to other mattresses. In general … I believe that many consumers have bought into the idea that more memory foam on top is “better” while I am of the opinion that most memory foam mattresses have too much memory foam on top and that the least amount possible is far better (less spinal alignment issues).
Even various layering mixtures of latex and memory foam in my opinion will feel and perform much better than most memory foam layers by themselves … although some of this is of course based on personal preference. I personally like an inch of latex over 2-3" of memory foam as it doesn’t have the same “stuck in the mattress” feel of thicker layers of memory foam. To make these types of constructions would usually mean working on a custom mattress with a manufacturer who does this. Many people would be very surprised at the value that can be obtained in doing this but it takes a real knowledge of what a person wants and “how to get there”. I built my own mattress layer by layer for example (including choices in each layer’s thickness down to 1/2 inch) and chose the quilting/ticking knowing how each choice would affect the rest of the mattress. I ended up with a mattress that had never been built “quite that way” before that was perfect for us. I still paid less than half of anything even close to equivalent that would be available at any local outlet.
For those who wish to order a memory foam mattress online when they don’t have access to a local manufacturer that is close enough to where they live, there are many options … but it is a little “risky” since there are many variables that need to be taken into account and I would certainly recommend field testing (especially with layer thickness) to get a sense of what will work. Sleepez for example sells 3 layer “choose your own layer” latex mattresses and he can include 5.5 lb Sensus as the top layer instead of soft latex. This would result in a mattress that had a memory foam comfort layer that could be customized for feel and support by choosing the latex underneath it. The wool quilting on top would result in less “sinking into” the memory foam while the latex underneath could be customized to alter the feel of the memory foam. IMO this would be superior to any Tempur mattress in terms of quality and the latex would certainly be superior to the materials that Tempurpedic uses in their support layers.
There is a small list of memory foam outlets in post #12 here which I will be adding to over time and posting in a more easily accessed location on the forum or the site as I talk with more online outlets and ask them my “list of questions” :).
Because of the variables and risks involved in buying memory foam online and the overwhelming misinformation and lack of transparency on most of the sites that sell online, I have avoided posting a lot of information about this as it can become rather overwhelming and confusing and I believe when it comes to memory foam it is much “safer” and more accurate to work with a local manufacturer where the mattresses can be tested and who knows how changing various layers or other options can affect the entire mattress. Memory foam mattresses can be much harder to “duplicate” than latex and polyfoam because its response varies so much with individual circumstances, layering, and between different foam formulations. I even believe that much of the current popularity of memory foam is based on a lot of misinformation and a lack of meaningful ways for consumers to compare memory foam with other materials that are superior in many ways.
Most people do not realize that memory foam is just a layer in a mattress that is combined with other layers to produce what they “feel”. Most also don’t realize that what they believe is so comfortable in the store may not feel so comfortable after they sleep on it for many nights and do not always relate the long term effects of their mattress choices to their aches and pains or lack of rest a few months later. This is compounded by the fact that in many cases, by the time people end up replacing their mattress … almost anything is an improvement even if it is nowhere near what they really need.
There are some sites however that are much more “helpful” than others and that offer various degrees of customization and knowledge and I will slowly add these as my conversations and research justifies it.
Thank you for the questions as it gave me a chance to explore a few ideas and to once again outline the benefit of working with a local manufacturer when possible where I truly believe the best service and value exists for any type of mattress.
If in my “wanderings” I’ve missed answering anything or if you need more specifics … feel free to ask
Phoenix