Hi missy_
Stearns & Foster doesn’t provide this information so it’s unlikely you would be able to find it. If you did you would almost certainly find that they are lower than the quality/density guidelines here. As you can see in the guidelines here … I would avoid Stearns & Foster completely along with any other mattress where you aren’t able to find out the quality of the materials inside it because you won’t be able to identify any weak links in the mattress or make meaningful comparisons to other mattresses.
You can see the specs of the Rhapsody Luxe (to the best of my knowledge) in post #3 here and there are no weak links in the mattress but as you can see in the guidelines I linked I would tend to avoid Tempurpedic as well because there are many other mattresses that use the same or better quality materials at much lower prices and which for most people would be much better “value”.
The first place I would start your mattress research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that you will need to make the best possible choices … and know how and why to avoid the worst ones.
Phoenix