Unfortunately it’s not possible to “diagnose” mattress comfort issues on a forum with any certainty because you are the only one that can feel what you feel on a mattress and there are too many unique unknowns, variables, and complexities involved including body type, sleeping positions, health conditions, and individual sensitivities and preferences that can affect how each person sleeps on a mattress in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your Personal preferences) or how they may affect any “symptoms” you are experiencing and a mattress that would be “perfect” for one person or even a larger group of people may be unsuitable for someone else to sleep on. Having said that … 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 more detailed information 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.
Resolving mattress issues usually involves a process of differential diagnosis that uses probabilities along with assessing how your symptoms change with each combination you try to help identify which “direction” of firmness changes or which combination of materials would have the best chance of success.
The most common reason for lower back pain is a mattress that has support layers that are too soft or comfort layers that are too thick and/or soft. When you added the additional soft layer it seems that your back “symptoms” became worse so this seems to be pointing to the most likely probability that the additional soft topper was moving you in the wrong direction and you may have needed either a firmer top layer, a thinner top layer, or a firmer support core although only your actual experience can know whether any combination of materials will work well for you because each person can be unique and may not fit the “averages” of what would work for others.
I would try turning the mattress upside down so you are sleeping on the 32 ILD layer and see how your back symptoms change with sleeping on the firmer side of the mattress. Your experience with this will provide the information and “feedback” from your body that you will need to help you decide on any additional changes that may be needed after that.
Perhaps most important of all though I would make sure you have a more detailed conversation with the manufacturer of your mattress who may also have some suggestions based on their experiences with other customers that are similar to you.