Hi unclecrystal,
You’re correct that it’s not possible for me to diagnose your issues online, but there is some information about the many different 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 to you.
You stated before you’re more concerned with comfort than support, and if you slept worse with a firmer layer of latex on top and slept better on a couch (which usually allows you to sinking more deeply), then it may be an issue that you desire a deeper “comfort cradle” and perhaps a slightly softer “transition layer” or a bit more plush material added on top could make a difference.
It’s usually the case when someone complains of low back issues that there is a lack of “deep support”, but this may not be your case.
You certainly can place your mattress directly upon the floor to see if that makes any difference for you. Most latex manufacturers will recommend a flat and firm slat surface that doesn’t bow.
Also, be sure that you’ve reevaluated your pillow thickness with your new mattress, as this can often be the cause of lower cervical/upper thoracic pains.
Phoenix