Hi ohmykitty,
I also wish that you could have found us before you made your purchase as well.
Unfortunately the specs you listed don’t contain any meaningful information about the quality or durability of the materials in your mattress (see this article) but with major brands it would be safe to assume that the comfort layers in your mattress use lower quality materials that would tend to soften and break down prematurely. The specs of a mattress also won’t tell you much about whether a mattress is a suitable match for you in terms of PPP and are only useful to assess the quality and durability of the materials and components in a mattress.
While it’s not possible to “diagnose” mattress comfort issues on a forum because there are too many unique unknowns and variables involved that can affect how each person sleeps on a mattress in terms of PPP (Posture and alignment, Pressure relief, and 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 make the types of changes that have the best chance of reducing or eliminating any “symptoms” you are experiencing.
Having said that … based on your description the most common reason for lower back pain is a mattress that is too soft and if I had to guess I would say that it sounds more likely that your mattress is too soft than too firm. While it’s fairly simple to “fix” a mattress that is too firm by adding a topper … it’s generally much more difficult to fix a mattress that is too soft because the best solution would normally be to remove the layers or components that are too soft and replace them with firmer or thinner layers. Having said that … there are some suggestions in post #4 here that may be helpful for a mattress that is too soft at least on a partial or temporary basis.
I would also check the support system under your mattress to make sure that there is no flex or sagging under your mattress which could also contribute to the issues you are experiencing as well. You can check to make sure that the support system is providing suitable support for your mattress by putting the mattress on the floor to see if there is any noticeable difference (and there shouldn’t be).
If none of the suggestions help or help “enough” for you to sleep well on your mattress … then you may need to start over again by selling your mattress and purchasing a new one that is more suitable for you or if there are no other alternatives and as a last resort before disposing of the mattress completely you could also try “mattress surgery”.
Phoenix