If you've been reading other saddle fit threads, you won't be surprised that the answer to "now what do I do" is you find a professional saddle fitter to work with. Ideally find an independent one (ie not a sales rep for a particular brand), or one who works with/in a large tack store that will have many saddles for you to choose from including used. Tree sizes are like women's clothes sizes--they give you some idea how big a thing is going to be, but that's about it.

Oh, and if you plead poverty over the saddle fitter, we'll sic StreetMutt on you ;-)