Hi Brick,
Outside of the Costco Topper … I’m still not exactly clear on what the ILD or the density of your layers are and I also don’t know anything about your height/weight or body type which would play an important role as well.
Trying to “diagnose” exactly what may be causing various issues unless they are very simple and easily solved when I can’t feel exactly what you are feeling, see you in person on the mattress, know your height/weight and body type, have more detailed information about the firmness of your mattress layers, or have a more detailed and “nuanced” conversation on the phone that could include much more information is much like a doctor trying to use a forum to diagnose a back issue or a mechanic trying to diagnose an issue with a car without being able to see and test what may be happening in person, and without enough information to really even know what may have the best odds of success. I just don’t have enough information to be able to “visualize” what may be happening.
The best I can do on a forum is to either suggest that you work with the retailer, provide some suggestions that may help in more simple cases or link you to information that can help you to determine what may be happening so that you can make choices based on your own “educated” intuition. In many cases … adding a topper can be a matter of trial and error because there is no formula that can take into account all the many variables or the many different causes for similar issues … especially when things seem more complex and may not have a single cause.
The simplest and often most effective option is usually to work with the odds and to look under the area where you are having the symptoms. If your arm for example is falling asleep this will usually indicate either a pillow issue or that the layers are too firm under the shoulders and cutting off circulation. Since you are still on the same top layer (although the Talalay layer underneath would soften it) this could still be the case. Of course there could be other more complex causes as well but these are outside the scope of a forum.
The 3" Talalay topper is certainly good quality but I don’t know if 28 ILD is firmer or softer than your old topper. Is there a reason you put this under your current topper instead of on top. Have you tried it on top?
I think that most of the suggestions I could make and ideas I could share that could help are already earlier in this thread. Toppers will often take some trial and error because there is no formula that can be used to choose them. They are used to add thickness/softness to the comfort layers and post #8 here has some generic guidelines that can help in most “simple” cases. If things are more complex and these don’t solve things … then either working with someone that can actually see you on the mattress and/or has the experience and knowledge to make other suggestions is the best way to go. The alternative is trial and error.
I also think that it may be worth considering the medium support core (based on your testing) although this too is just a shot in the dark because I don’t know if this may be a suitable choice without knowing more about the core density/ILD of the layers or about you as well.
My tendency would be to have a long conversation with John along with some extensive testing of other layers, tell him all the “symptoms” you are dealing with and that you are not happy with the mattress as it is … and then ask him for his best suggestions about what is possible to change in the mattress and which changes he thinks have the best odds of success … and why.
Overall it sounds to me like you need more “softness” in the mattress (in either the comfort layer or support layer or even both) but again this is just a guess because I really don’t have enough information about whether going softer in one or both layers would be suitable for your weight and body type.
Phoenix