Welcome to the Mattress Forum!
I’m sorry you’re having some back pain issues adjusting to your new mattress, but unfortunately there are entirely too many “it depends” as to what may be causing your issues, and there’s quite a bit of information you’ve left out, so I can only offer general guidance, which hopefully you may find helpful.
You didn’t specific how long you’ve had your new mattress, only that it’s “recent”. There will always be a “period of retrogression” where it normally takes someone time to adjust to their new product, and this can depend upon the old mattress and it’s level of support and comfort (and this would have an impact upon your “learned alignment” that you might need to overcome), your own level of flexibility and strength, and your particular sensitivities, among other things.
Also, you don’t state what your mattress is being placed upon, so you should be sure that your foundation meets with the requirements of Cozy Pure and that it is a flat and firm surface and not allowing the bed to sag, which could contribute to back issues.
You didn’t mention your preferred sleeping style (back, side or stomach) and this can also have an impact upon the comfort layers selected with a mattress. Apparently you (or Cozy Pure) thought that your situation required a bit more surface comfort with the additional of the 2” latex layer (you didn’t mention the density of each layer you currently have). Side sleepers generally require a slightly softer sleeping surface comfort, prone sleepers generally require a bit of a harder surface comfort, with back sleepers generally somewhere in between. This will also vary with somatotype and BMI (those with a higher BMI generally require firmer and more substantial layers).
People’s definition of “pain” can be quite varied, and there is some information about the many different “painful” symptoms that people may experience on a mattress and some of the most common causes behind them in post #2 here that may be helpful. Pain, such as pressure point discomfort, can often be from a lack of surface comfort. Pain, as in low back alignment pain where it is difficult to “straighten up” in the morning, is often from a lack of deep support. The two basic functions of a mattress are to provide deep support/alignment, and then to provide surface comfort, and I personally recommend to start with alignment/support, then surface comfort. In general … what you would be looking for is a mattress with firm enough deep support and then comfort layers that are “just enough” in terms of thickness and softness to “fill in” and support the more recessed parts of your sleeping profile and relieve pressure in your most pressure prone sleeping position (usually side sleeping for those who sleep in this position) so that there is less risk to alignment in your other sleeping positions.
I know much of this information is more “general” in nature, but that’s about the best I can offer with the information provided. My overall best suggestion is a personal consultation with the people at Cozy Pure, as they are very knowledgeable about latex designs and I do think highly of their product knowledge. They will know best about their products and what choices may serve you best with your current set up.