Hi LisaD,
I hope you have success with your neck issues … dealing with back or neck issues can be both frustrating and complex as you know.
Based on your feedback though it seems that the Pamper by itself is fairly close. With your longer and lighter build the 2" of soft latex may be “just a little” too thin but would be more likely to be suitable than it would be for someone who was heavier. When you are on your side you may be “twisting” away from pressure issues as a result of your shoulders “going through” the softer layer and “hitting” the firmer latex underneath and this may contribute to the upper back pain. As you mentioned it could also be connected to your neck issues because upper back and neck issues are often connected to a pillow.
A body pillow may also be worth considering because it can help with alignment and “twisting” with side sleeping.
If your symptoms are primarily connected to your upper body and neck I would focus more on the neck and pillow and consider a topper in the range of 1" - 2" and focus less on the lower back or pelvis area which is probably OK. If you choose memory foam I would make sure it was at least 4 lbs density and if you are OK with a little firmer feel then 5 lbs would be more “supportive”. If your memory foam topper is low density then you may be sinking into it more and your pillow may be holding up your head too high which could contribute to the neck issues. The more you sink into a mattress the less the gap becomes between your head and neck and the mattress surface and the thinner the pillow you need to keep your head and neck in good alignment.
There are some topper guidelines in post #2 here and the posts it links to that can help you use your experience on the mattress by itself as a reference point for the topper firmness and thickness that may be most suitable.
When you sleep in multiple sleeping positions then a pillow that can be scrunched and change shape can be useful. As you know side sleeping generally needs a thicker pillow to keep your head and neck in alignment than back sleeping which generally needs a little thinner and some support under the cervical spine. If you like a more resilient “feel” then shredded latex may be worth considering. The pillow thread here may also have some links and information that you may find useful.
It can take some detective work and trial and error to isolate the underlying cause of complex issues and decide on which changes have the best chance of success but to the degree that any mattress or pillow can help with medical issues it’s certainly worth the time and effort.
If you make small incremental changes with a “plan” in mine, make sure that you test each change for long enough that it is more predictive of your longer term experience and not just the result of the many day to day variables that can affect your sleep, and carefully compare the results of each change with the last one to see which “direction” you are going in terms of degree of improvement, then your odds are much higher of finding the best possible mattress / topper / pillow combination.
Phoenix