Hi llong,
I believe that their topper may be 24 ILD but none of the stores have ever been able to confirm this for me (and I’ve asked many of them). ADDED: you can see the specs here (thanks djarchow) and the topper is 14 ILD.
[quote]This bed eliminated the lower back pain (EUREKA!) but now have upper back pain and a very sore neck. I went back in and they talked me into buying a different pillow to see if that helped.
It hasn’t but I am so thrilled at the lack of lower back pain I want to see if I can tweak this mattress to work.[/quote]
Post #2 here and the posts it links to has more information about the more common sleeping “symptoms” and some of their possible causes but with the symptoms you are describing your pillow is also the first thing I would have suspected as well.
Side sleepers generally need a thicker pillow to keep their head and neck in good alignment, stomach sleepers generally need a very thin pillow or no pillow at all, and back sleepers are in between these two. There is more about pillows in the pillow thread here.
I don’t know your body type but it’s also possible that the topper in combination with any softer comfort layers in the mattress may be a little too thick and/or soft for you which can lead to sleeping in a more “hunched” position when you are on your back which can also lead to upper back discomfort or pain.
I don’t know the cause of your knee pain but sleeping with any joint outside of it’s “neutral” range of motion can certainly cause pain in that joint (see post #2 here). As you mentioned, a pillow between the knees can also help when you are side sleeping.
Phoenix