Hi Chad,
Unfortunately this is all too common with major brand mattresses that use lower density foams and develop soft spots (or “virtual” impressions) even though there are no visible impressions when you are off the mattress. My guess is that the memory foam and the base layer may both be fairly low density which leads to more rapid softening (without actual impressions so this isn’t a warranty issue).
It’s also quite possible that you mattress is not suitable for side sleeping for you because if the support core is too firm then with only 2" of memory foam you would likely “go through” it and the firmer foam underneath it could create pressure points on your side. In other words … you could have two separate issues … one with the original design of the mattress which has comfort layers which are too thin for you and one with foam softening which leads to alignment issues on your back
A topper can be an effective solution for a mattress (or a futon) that is too firm if you need some extra pressure relief on your side but it’s not generally an effective solution for a mattress that has developed soft spots because the topper will just follow the soft spots underneath it and can even make the problem worse (your heavier pelvis could sink down even further before it reached the firmer support core).
If the softening is very slight then a topper may work or at least “hide” the symptoms for a while until the foam underneath it softens further (although the topper can slow this process down).
As a stopgap measure you could turn the mattress over and add a slightly thicker topper to the other side using the topper guidelines.
A 3x3" latex mattress with soft talalay on top and medium and firm Dunlop in the bottom two layers is a configuration that works well for a fairly wide range of people and of course there are many other configurations that can match your needs and preferences in terms of PPP as well. Post #2 here has more about making comfort and design choices.
The choice of material is strictly a personal preference but no matter what materials you prefer in a mattress or which design works best for you … it’s important to make sure that the quality is high enough that early foam softening and the loss of comfort and/or support that goes with it isn’t likely to be an issue…
Phoenix