Hi jwjojo,
The closest site members who carry latex mattresses I found to your location are:
Comfort Sleep Systems in Branford, CT.
Nest Bedding in NYC.
Scott Jordan Furniture in NYC.
Shovlin Mattress Factory in Fanwood, NJ.
Urban Natural Home Furnishings in Paramus, NJ.
While I don’t keep track of the specific items (i.e., latex) that other retailers might have on the floor, in northern New Jersey you may wish to look at either the Monroe Township/Newark list in post #7 here or the New York City list in post #2 here.
If you are not staying local with your purchase, you may wish to look online and use the experience and expertise of the members listed in post #21 here who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
Yes, for someone sleeping in the prone (stomach) position, something with a firmer surface comfort and better deep support is generally advised. Post #2 here has some generic guidelines for different body types and sleeping positions.
Phoenix