You may already some or all of the following, but I will say it anyway.
There are several widths and aspect ratios for a given size.
Reccomended rim width range for a specific size is not the same from one mfg to another because tire construction varies.
Using a rim that is the maximum mfg recomended width for the tire size makes it more difficult for the mech to mount and for the owner to keep the beads seated.
The bigger the tire is for a given curb weight, the lower the operating pressure will need to be. Lower pressures do not help bead seating.
If you are set on 9" rims, go to tirerack or discount tire and find their mfg links. Each mfg will have a single page chart for each tire model listing all the sizes and the reccomended rim widths. Try to find a tire that is reccomended for up to a 9.5" rim, then search tirerack for that size. Check the mfg chart for the reccomended widths on the tire before buying.
Here is BFG's chart on a Radial TA:
http://www.bfgoodrichtires.com/specs/radial-t-a/12.html