My general preference when buying guns are ones that are still in production, or at least guns with a wide availability of parts and mags.

With that in mind, if I were in your position, I'd lean towards a Kahr K9. The P9 is actually on a short list of 9mm guns I'd like to get. While I haven't tried every striker-fired gun under the sun, the Kahrs I've tried had the best triggers, reminiscent of a very smooth, light DA revolver.

If you're ok with SAO, 1911-style guns, the Springfield Armory EMP and Sig P938 could be good options. I believe Kimber makes a version of a 9mm-specific, downsized 1911-style gun, too. If you have the budget for them, I believe both Wilson Combat and Ed Brown make high-end versions.

Both the Sig P239 and Beretta 92 Compact M are guns I'd really like to get, and are excellent guns, but they may be a little larger than your size parameters. And they're out of production. While parts may not be an issue, getting mags can be a problem, especially with the 92 M. I consider mags to be consumables, so being able to easily replace them would be a factor for me.

Just my opinion.