Hi soxfan,
When you are first sleeping on a new mattress it’s fairly “normal” to be overly aware of every new sensation that you experience and I would give it things a few weeks so your mattress has a chance to break in and you have the chance to adjust to a new sleeping surface before considering any changes or “fine tuning” of your mattress (see post #3 here).
It’s possible that when you assembled the mattress that the latex wasn’t laying flat and you may need to “wave” the layers into position so they are lying more evenly (see the assembly videos that are linked in post #12 here). It’s also possible that the edge firmness could be the result of some flex in the middle of your platform bed.
Again I would give it a few weeks before making any changes because any initial “symptoms” can be the result of your body needing some time to get used to sleeping on a different mattress that is different (or softer) than the one you you were used to.
If after that you are still experiencing some soreness in your lower back (or other “symptoms”) then the first thing I would suggest is a conversation with SleepEZ to help you decide on the the changes that would be most helpful. The most common reason for lower back issues is a mattress that is too soft and allows the hips/pelvis to sink down too far so you may need some additional firmness or support under your lower back. If this is the case then the first thing I would try would be to put the firm Dunlop layer in the middle and the medium on the bottom to firm up the support under the heavier parts of your body.
Phoenix