Hi JJR,
The first step would be to decide whether you believe you need more softness or more firmness because this is something that you are in the best position to assess and I don’t have a clear idea of which “direction” would help you most. I also don’t know your weight or body type, your dominant sleeping positions, how long you tend to spend in each position, your sleeping history or any health conditions that may be a factor, whether you tend to experience similar symptoms on other mattresses or how they or other mattresses that you sleep “symptom free” on may compare to the tranquility, or how much your experience on the mattress has changed over time compared to when it was new. Your feedback and symptoms also seem to be pointing in two different directions.
If you believe you need more softness and pressure relief (which some of your feedback seems to indicate) then a topper would be a good option to add additional pressure relief to your mattress.
If you believe that the mattress is too soft (which some of your feedback also seems to indicate) then it would be much more difficult to “fix” because this would normally involve removing and replacing layers rather than adding a topper on top of them. There are a few suggestions in post #4 here that may also be worth trying that can sometimes help … at least to some degree … with a mattress that is too soft or is sagging (either sags that are visible when you are off the mattress or that are “virtual” and only happen when you are on the mattress).
I’m also not familiar with the mattress so I don’t have a good frame of reference and some of your feedback is “pointing” in opposite directions. “Symptoms” like these …
… are usually “pointing to” the need for some additional softness. Some of your earlier comments seem to point in this direction as well.
"Symptoms like these …
… are usually pointing to a comfort layer that is too thick/soft or a support layer that is too soft.
I also don’t know the firmness of the layers or materials in the mattress but typically a 3" memory foam layer with a reasonably firm support core would be on the firmer end of the scale and their mattress comparison chart (the link is on the top of their page) indicates this is one of their firmest mattresses as well (which would imply that it may need more softness for many people) but in the comments about this mattress they also indicate that it’s a close comparison to the Tempurpedic Cloud Luxe which is the softest Tempurpedic mattress and would “point to” the possibility of needing a firmer mattress. Of course your weight will be a big factor in how firm or soft a mattress will be for you because higher weights will sink into a mattress more deeply so it will feel softer than the same mattress would feel for someone that was in a higher weight range.
It’s also possible that you may need both firmer support in the polyfoam support core and a softer/thicker and more pressure relieving comfort layer.
Heat issues and the tendency for memory foam to become softer over the course of the night and some degree of motion restriction are all fairly typical of most types of memory foam … especially in thicker layers … although they will affect some people much more than others. This may also be pointing to the mattress being to soft for you because if you sink into a mattress more deeply then the foam would be more insulating and can sleep warmer.
It would have “some” effect on reducing the heat that reaches the memory foam which can firm up the memory foam (but not the polyfoam support core) to some degree or at least slow down how long it takes for the memory foam to soften with your body heat yes … but how much the effect will be can only be known based on your actual experience because there are many variables including the specifics of the memory foam and how temperature sensitive it is (how much it changes in response to changing temperatures), the basic firmness of the memory foam (3 lb memory foam tends to be softer), your body type and weight distribution, the variations in your sleeping positions, how much time you spend in each position, how much heat you generate when you sleep, and on the specifics of a topper you use.
If you are in a trial and error mode then I would at least start with toppers that you are more familiar with and that have a good return policy so that if it doesn’t do what you are hoping it will do that you don’t start accumulating toppers that you can’t return … and the expenses that go along with this. A wool topper will also tend to be firmer than softer foam layers … especially as it compresses over time … so it may be firmer than you hope for (although wool is very temperature regulating). Again this is something that you will need to try before you know whether it will do what you hope it will do.
I would only do mattress surgery as a last resort if there were no other options available to you and I certainly wouldn’t go in this direction until you had more clarity about the effect of some of the other changes or toppers that are available to you. This is something that only you can decide but if you do decide to go in this direction then there is more about mattress surgery in post #2 here.
I would start by adding a foam topper (either polyfoam, memory foam, or latex) that you can return so you will have a better frame of reference about how it affects your sleeping experience and “symptoms” and then you can use what you learn from your experience with a specific topper as a starting point and what it seems to “point to” to decide whether to return it and try something else that was either thicker or thinner or softer or firmer or perhaps a different material.
I would also strongly suggest that you have a more detailed phone conversation with Bedinabox about your experience because they will be much more familiar with the specifics of their mattress than I am and will likely also have had experience with customers that have a similar body type and sleeping positions as you and were experiencing similar symptoms and the type of fine tuning that was able to help them.
Phoenix