Hi digitaldave,
It’s not really possible for me to know what the cause of your symptoms may be because I can’t feel what you feel or see you on the mattress but there is some information in post #2 here that talks about the more common symptoms that people can experience on a mattress and some of the possible causes for them but most symptoms can have multiple causes and if simple solutions that would generally work for most people don’t work for you (such as adding the topper) … then trying to “diagnose” the types of changes that may be most beneficial to you can be more complex and the best approach with these types of more complex issues would be a more detailed conversation on the phone and possibly another visit to test different combinations in person.
In general terms though … the most common (but not the only) cause for lower back pain is either support cores that are too soft (which wouldn’t be the case with your mattress because it’s very firm) or comfort layers that are too thick and soft for your body type or sleeping positions both of which can cause your hips/pelvis so sink in too deeply and “tilt” which can put your lower back out of alignment.
I talked with John and he said that all their floor models are the same as the mattresses that their customers receive and they all include the fire barrier for that particular mattress. As you know this can be removed for those customers where the fire barriers are causing an issue with comfort or at least to test and see if removing it makes a difference.
It sounds to me like you may have chosen a mattress that was more suitable for exclusive stomach sleepers but would be too firm for most people that spend much time sleeping on their side and that your testing didn’t effectively predict your sleeping experience. it may be a good idea pay them another visit so you can very carefully test different combinations in all your sleeping positions (using the testing guidelines in the tutorial post) to see which combination of materials would be a better match for you.
As you know they allow for one free layer exchange with a mattress and the after that they only charge the cost of the materials for any further changes. I think that when you are facing more complex issues though that the best idea would be to first talk with John on the phone so you can explain your experiences in more detail (both on the original mattress and with the topper) and he can explain the options you have available that along with more careful testing (if you visit them again) would give you the best chance of success. They would be much more familiar with their own mattresses and the options they have available that can help with any issues you may be having than anyone else.
This would be typical of a zoned core or layer yes. There is more about zoning in this article and in post #11 here. Zoning is often helpful because it can help to “hold up” the heavier parts of the body more effectively (such as the hips/pelvis) while at the same time “allowing” the wider and lighter shoulders to sink in more deeply so you sink into a mattress more evenly which can help with alignment but like any mattress design, what works well for one person may not work as well for someone else because each person is unique. The “bottom line” … no matter what the design of a mattress … is always whether your testing or personal experience indicates that a mattress is a good match for you.
Phoenix