Hi church11,
Post #11 here has some links to posts about the more common types of gel materials, some more technical information about thermoplastic gel itself, and some thoughts about the newly emerging gel materials as a group.
Yes … their Cirrus is designed to be the closest of their models to the Tempurpedic Cloud Luxe in terms of feel and in the quality and design of the materials and layers that are used to achieve the feel as well. Of course this would be assuming that the Tempurpedic Luxe has completed it’s break in period and that the Cirrus has as well (they will both be firmer until the foams have completed their initial softening).
Unfortunately there is no “formula” that can predict which mattress may be most suitable for your needs and preferences except in the most general of terms and your own local testing along with more detailed conversations with any manufacturer you are considering (who are much more familiar with all the details of the mattresses they make and which ones may best match the body types and sleeping styles of different people) is much more accurate than any theory at a distance I could provide. In general terms this could be a good candidate for a heavier side sleeper that needed or preferred a softer comfort layer. If you have tested the Tempurpedic Cloud Luxe and it worked well for you (assuming it was tested “accurately” and you spent enough time on the mattress fully relaxed) then that points to this being a good choice as well.
What comes through your comments (which are too complex and non specific for me to really gain any more specific insights from them) is that you need a thicker softer comfort layer for your wider shoulders and then good support that will “stop” your heavier parts from sinking in too far past the comfort layers and this seems to be in the range that could accomplish this.
Low back pain relief … to the degree that any mattress can help … would be helped by a mattress that kept you in good alignment in all your sleeping positions. This wouldn’t depend on the materials as much as the design of the mattress and how well it matched your specific needs and preferences regardless of materials. It is a common myth that one type of material or another is "better’ for backs or for back pain when in truth it depends on the mattress design more than the materials used in the design.
Some of the better value memory foam options I’m aware of are listed in post #12 here. I think each of them has their return policies listed on their site but if not a quick call will find out for sure (I don’t have the return policies in the notes I keep about each one because they are usually easily available). A call to any of them that interested you would give you more information about how any of their mattresses may compare to various Tempurpedic models but Select Foam is a little more specific in their designs in terms of matching the “feel” and matching (or bettering) the quality of materials and the design and layering as well. They have their mattresses side by side with the Tempurpedics at their bricks and mortar store and use this ongoing customer feedback in their designs.
I like some of the Restonic Tempagel mattresses and in some cases they can be better than average value as well (their gel memory foam is good quality) but the only way to know how well they may match another mattress or your own needs and preferences would be through personal testing as well and if you have all the details of every layer then you could make more meaningful quality and value comparisons between them as well.
Phoenix