Hi Mamie,
In case you haven’t read it already, I think the first place I would start is the first post in this very thread which will give you all the basic information you need to help you make some very good choices (and eliminate the worse ones like Serta and Tempurpedic).
Not only have I heard of them but I think highly of Mark and the quality and value of the mattresses he builds.
Some of the better options and possibilities in the NYC area are listed in post #2 here (and post #7 here has a more categorized list with more details about some of them) and Dixie Foam is certainly one of the best options on the list in terms of the quality, value, and service they provide.
A forum search on Dixie Foam (you can just click this) will bring up more forum posts and information about them.
Connecting with local “experts” in combination with good testing is always the best way to choose a mattress that relieves your pressure and keeps you in good alignment in all your sleeping positions (which are the two basic functions of a mattress) which is especially important for anyone with back issues.
Phoenix