Hi curmudgeon,
Smart latex is mostly synthetic latex. It’s a good quality material compared to other types of foam but it’s a lower cost version of latex. Hypersoft is a lower density polyfoam which would be a weak link in the mattress and which I would avoid in any thickness more than around an inch or so because of the risk of foam softening and the premature loss of comfort and support (which isn’t covered by warranty unless there are also visible impressions more than the warranty exclusion which is not that common). In the case of the Stearns & Foster luxury latex mattresses you are sleeping more on polyfoam comfort layers than on latex and there are many reports of these types of mattresses having foam softening issues in the 3 - 5 year range … and often sooner. As you may already know from some of the other posts on the forum (particularly the tutorial post here and the mattress shopping guidelines here) … I would certainly avoid this type of mattress and all the major brands such as Sealy / Stearns & Foster both because they are not generally good value and because they don’t disclose the density of the polyfoam they use in the comfort layers which are usually the weak link of a mattress (and they are generally in the 1.2 - 1.5 lb range which are not good quality or durable materials).
You can find all latex mattresses that use much more costly versions of latex (such as 100% natural Dunlop or Talalay latex) in the same price range which have much better value and don’t have the weak links of a latex mattress that uses too much lower density/quality polyfoam in the upper layers.
Most people use an adjustable bed for personal reasons (such as reading in bed, watching TV, or for the other features such as massage) but you’re right that in most cases raising the head or foot would be most suitable for back sleepers who could benefit from raising the head or foot of the mattress. Raising the head can help with things like snoring or acid reflux conditions and raising the foot can help with pressure and tension on the lumbar spine or circulatory issues (much like a pillow under the knees for back sleeping). A small amount of elevation in the foot of the mattress is usually still OK for side sleepers and can help with lumbar tension for back sleeping as well but too much can cause alignment issues for side sleeping and for stomach sleeping it’s not generally a good idea to elevate either at all. There is more about adjustable beds in post #3 here and the adjustable bed thread it also links to.
Phoenix