Hi Petschauer,
The list of outlets in post #7 here should help you find some outlets that carry latex mattresses either in the comfort layers or the support cores or both. There are a few other NY lists as well but this one is a bit more narrowed down.
This should also give you a chance to test various latex ILD’s in the comfort layer to confirm that n4 (@ 30 - 34 ILD) is suitable for what you need and prefer since it’s firmer than most would choose.
I would include mattresses that have latex over other support cores (such as innersprings or high quality polyfoam) because this will also give you valuable information about how latex feels and performs in the comfort layers as long as there is no more than an inch of polyfoam over the latex.
Hopefully this will give you some latex to test to help you get a general sense of the type of firmness and layering that works best for you.