Hi MeddlingKids,
There are so many variables and possibilities (including body type, sleeping positions, and your own unique physiology) that it can be difficult to track down the underlying cause of any “symptoms” that someone experiences on a mattress but the “standard” Tempurpedic Cloud has 1.2" of extra soft 4 lb memory foam over 1.6" of 5.3 lb memory foam for a total of 2.8" of memory foam which is thinner than most of the Tempurpedic mattresses so the odds are much more likely that you need a little bit of additional softness but as Everready073 mentioned there is also a good chance with pain or discomfort in between the shoulder blades or in the upper body that your “symptoms” could also be connected to your pillow. Post #2 here has a little more about some of the more common “symptoms” and ideas about what may resolve them. Post #2 here has more about some of the things to check for and that can help with a memory foam mattress that is too firm.
If you did need more softness and a different pillow (or some of the other suggestions) don’t resolve the issue … then as Everready073 also mentioned it’s usually best to use the thinnest possible topper (using the topper guidelines here) that are “just enough” to provide good pressure relief in all your sleeping positions because the thicker and softer the topper the greater the odds that you will exchange a pressure issue with an alignment issue (which seems to have happened in your case). Even though the Cloud mattress has relatively thin layers of memory foam … adding 3 more inches of softer 4 lb memory foam on top of a mattress that is already in the “soft” range would have much higher odds of producing the alignment symptoms you are experiencing and it would be safer to use a thinner topper that was “just enough” to add the additional softness and pressure relief that you need and no more.
Phoenix