Hi paladin732,
I think the first place I would start is post #1 here which will give you some of the basic information, steps, and guidelines you will need to make the best possible choices. One of the links in the post is to this article which will help you avoid some of the low value choices such as the major brands (including Tempurpedic). There is also a lot of information it links to which will help answer many of your questions.
The quality of any mattress is as good as the materials that are inside it regardless of the label on the mattress. You can see my thoughts about Joe and Nest Bedding in the San Francisco list here. I think their own component mattresses use good quality materials but I am not a fan of the bedinabox they also carry because of the low density of the memory foam they use (see post #2 here)
I think that layered component mattresses with a zip cover are anything but a gimmick. they allow you to clean or replace the cover and they also allow you to re-arrange layers to change the feel of your mattress as well as exchange or replace individual layers that wear out faster without having to replace the entire mattress. They are great option IMO and many of the manufacturers that are members here and other manufacturers I respect as well use a similar concept.
Again … the quality of a mattress is only as good as the materials inside it and if the materials are similar then the quality of the mattress is similar as well. Select Foam use similar designs and the same or better quality materials in their mattresses as tempurpedic. Dreamfoam (Brooklyn Bedding is the manufacturer of these) also have some mattresses that use similar quality memory foam but again you would need to make a mattress by mattress comparison to make meaningful comparisons in terms of quality and value.
The issue of memory foam being toxic is a complex one and each person may have a very different answer to “how safe is safe enough for me?”. Post #2 here has much more information about this for those who want to do more detailed research into the safety of the different types of materials and components that are used in mattresses.
Yes … the breeze uses a gel infused foam (more like some gel sprayed onto the memory foam) and also has a “cooling” cover.
A forum search on Dreamfoam or on Ultimate Dreams will bring up dozens of posts with feedback about them. Most people seem to agree that their 13" gel memory foam mattress has a “feel” that is similar to but a little firmer than the Tempurpedic Cloud Luxe. The quality of the foams are a little lower (4 and 5 lb memory foam instead of 4 and 7 lb memory foam and a 1.5 lb base layer (although Tempurpedic may also now be using lower quality foam in their base layers compared to what they were using previously).
They aren’t in the same price range as Tempurpedic … they are significantly less. They use the same or better quality materials as Tempurpedic in all of their mattresses and they put unusual care into matching the “feel”, the quality of the materials, and the design of the Tempurpedic mattresses (not just the feel) at a significantly lower price. In other words they have much better value than the tempurpedics line. They are a member of this site which means that I believe they are among the best quality/value in the country.
Brooklyn Bedding is the manufacturer of the Dreamfoam mattresses on Amazon and they also have their own mattresses on their own site which have exchangeable layers as well although they are different designs. They are also a member of this site which means that I also believe they are also in the best quality/value in the country.
You can look at the details of their mattresses and the materials and components in them on their site as you can with Nest Bedding as well (or other manufacturers as well) which is how you make “apples to apples” comparisons between mattresses.
It would also be a good idea to talk in more detail with each of the manufacturers or retailers you are considering and ask them any specific or more detailed questions you may have. They are all open about what they do, the materials in their mattresses, and the benefits of their specific designs.
Phoenix