Hi franticvike.
Belated Welcome to our Mattress Forum! 
and thanks for your follow-up with your new mattress.
The 12" Hamq pillow top mattress has been rated as medium firmness on their own website, but of course the feel and level of comfort/support is very subjective as only you can feel what you feel on the mattress and there are too many variables and personal preferences involved to trust their firmness rating as an indicator of suitability for you. The mattress is using pocket coils as a base and poly and memory foams top layers and it has been previously discussed on our forum here
Your experience is fairly normal because any new mattress will have the foam slightly softening, as well as some adjustment coming from the fabric covering of the mattress which can take a few weeks to break-in. It can be different for different people, body types, and sleeping positions but the initial break in period can be anywhere from a few weeks to 90 days or so depending on the person and on the type of materials in the mattress. The mattress “breaks-in” a bit, as well as you adjusting and losing some of your own personal “learned alignment”.
There are still quite a few chemicals involved in the production of polyfoam, and the fact that a foam pourer uses some plant-based polyols (most these day do) doesn’t necessarily make it less “smelly”. Post #2 here has more details the use plant based polyols in polyfoam.
This sounds like a good plan…especially as you already have a latex layer to experiment with.
I look forward to your follow up after you’ve slept upon your mattress for a while longer.
Phoenix