Hi jh101992,
You may want to read this first (if you haven’t already). TMU recommends that the memory foam layers be at least 4 to 5lb density for increased durability. Here are more guidelines for purchasing memory foam in post #10 here
A 6" HD or HR mattresses in firm is suited for stomach or back sleepers.
If you occasionally sleep on your side then a 2" topper (memory foam, latex or HR foam) will help reduce pressure points on hips and shoulders. Both the 2 lb HD and 2.75 HR will provide exceptional support it’s important to note that the HD will be a little stiffer, and the HR a little more resilient.
Did I answer all your question?
Please let me know if you need any further information.
All the Best!
Mario