Definitely go with the Standard size waist. I have a 35"-36" waist and opted for the STTP which was a mistake. It fits, but I am only using about 1" of Velcro. I don't feel that it is as secure as it could be.
Also, Many people find that the smartcarry is more comfortable sitting down on their hips rather than right on their waistline. Your hips are probably a little wider than your waist.
I carry a MK9 which is the same size as your PM9 in a Standard Model/STTP/Small smart carry. If I were ordering again I would get the Security V/STANDARD/Medium smart carry so that I could use the holster for a little larger gun on occasion (ie: Glock 19).