Hi ClaireB,
The first place I would start your research (in case you haven’t read it) is post #1 here which has all the basic information, steps, and guidelines that you will need to make the best possible decisions.
I’m sure you have also seen most of these as well but a forum search on Prana (you can just click this) will also bring up more information about them and my thoughts about the thick polyfoam layer they use on top of their mattress … and of course their “value”.
Post #5 here and post #2 here have links to several posts that include most of the better options in your region that I’m aware of.
Phoenix