Hi indigogirl,
Just in case you haven’t read it yet … the tutorial post here has all the basic information, steps, and guidelines that can help you make the best choices. When you are looking at more specialized or specific criteria then the knowledge and experience of the retailer of manufacturer you deal with can be one of the most important parts of a successful purchase.
Post #2 here and the links it includes also has more information about the often confusing and conflicting information that you will encounter about chemicals and fire barriers in a mattress and natural, organic, and “safe” materials (they are not the same thing and there are synthetic materials that may be just as “safe” as organic materials) so you can answer the question of “how safe is safe enough for me?” based on the criteria that are most important to you.
You can read more about the Prana mattresses in post #3 here and in this thread. While it depends on the specific model … most of them use fairly thick layers of polyfoam in the top layer of the mattress over the latex.
If you let me know your city or zip code I’d be happy to let you know of any of the better options or possibilities I’m aware of in your area.
Phoenix