Hi Sleepy Will,
Just in case you haven’t read it yet … the first place I would start your research is the tutorial post here which has all the basic information, steps, and guidelines that can help you make the best possible choices … and know how to avoid the worst ones (and hopefully stay out of most chain stores as well).
The better options and possibilities I’m aware of in the New York City area are listed in post #2 here and there is also a more categorized list with more detailed descriptions of some of them in post #7 here.
The tutorial post also includes a link to a list of the online members of the site and many of these sell latex mattresses that include a wide range of different designs, options, and price ranges.
Phoenix