Hi handorson,
Tempurpedic used to disclose the details of their materials and they are still available in some places around the web (such as here) if you can get past all the sites that don’t include them any more. Their Tempur ES is (or at least was) 4.1 lbs and their Tempur material is 5.34 lbs (and also has softer and firmer versions) and their Tempur HD is 7 lbs. Their newer mattresses that they released after they began to remove the specs on their site and from retailer sites around the web are a little more difficult to find and in some cases aren’t available at all. Sometimes foam specs are available if you search for the few retailers that include them (or some of them), find alternative sources, do some calculations based on shipping weight, ar sometimes it can take some “inside” knowledge from sources that aren’t publically available at all.
Some of the better options in the St Louis area I’m aware of are listed in post #6 here and this thread with some St Louis feedback may be helpful as well.
Phoenix