Hi bear,
While it’s not possible to “diagnose” mattress comfort issues on a forum with any certainty because there are too many unique unknowns, variables, and complexities involved that can affect how each person sleeps on a mattress in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and your Personal preferences) or any “symptoms” they experience … there is more about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”.
These posts are the “tools” that can help with the analysis, detective work, or trial and error that may be necessary to help you learn your body’s language and “translate” what your body is trying to tell you so you can identify the types of changes that have the best chance of reducing or eliminating any “symptoms” you are experiencing (at least to the degree that any symptoms are from your mattress rather than the result of any other circumstances or pre-existing issues you may have that aren’t connected to a mattress).
The most common reason for lower back pain is usually a mattress that has comfort layers that are too thick and/or soft or a support core that is too soft but I would keep in mind that if your back pain doesn’t go away after you have been up for a while and have had a chance to stretch and limber up your muscles a little that it may be “pointing to” a pre existing condition and may not only be connected to your mattress. On the other hand a mattress that only has a 1.5" softer comfort layer would also reduce the likelihood that your mattress is too soft as well although the layer thicknesses you listed don’t add up to 10".
A topper is not a particularly effective way to “fix” a mattress that is already too soft or that has developed soft spots or sagging and at best it may provide a temporary or partial solution and at worst it can make some of the issues you are experiencing worse (if you are adding a soft topper to a mattress that is already too soft). If you add a firmer topper to a mattress that is too soft then the new comfort layer (the firmer topper) may end up being too firm to be comfortable for you to sleep on AND the topper will usually still “bend” or compress into the layers underneath it that are softer or have developed soft spots or are sagging so you can end up with BOTH comfort layers that are too firm and uncomfortable and support or transition layers underneath it (that were meant to be softer comfort layers) that are too soft to provide suitable support underneath the topper.
The most effective solution for a mattress that is too soft (either comfort layers that are too thick/soft or support layers that are too soft) or has developed soft spots or is sagging is to first identify the layers that are the cause of the issue and then removing and replacing layers that are too thick/soft or that are sagging (outside of replacing the mattress or course).
Having said that … there are also some suggestions in post #4 here for a mattress that is too soft that can sometimes be helpful. It may be worth trying your mattress upside down along with your topper to see if it makes any difference with your back pain which may help you assess whether your mattress is too firm or too soft.
As you mentioned the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort” or PPP or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, or “theory at a distance” that can possibly be more accurate than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
I’m assuming that you’ve read the mattress shopping tutorial here but two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists (based on all the parts of your personal value equation that are most important to you).
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart (which would certainly include Cozy Pure) and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else.
Phoenix