I've been studying this exact subject as of late. My Springfield XD-40 subcompact is too thick to be comfortable for me to conceal IWB (in waist band). Here's what you seem to be looking for: a 9mm or .40S&W single stack with thin profile grips. The Rohrbaugh has been mentioned, but last I checked, they run around $900-$1000, if you can find one. The Walther PPS 9mm is .91" wide at the thickest part of grip compared to about 1.25" for a Glock, XD, or 1911 with standard grip panels. The PPS doesn't excite me for some reason. It's not pretty to look at, and the ergonomics, especially the magazine release, look uncomfortable.
The Sig 239 is a single stack 9mm. It looks like heaven and probably shoots like heaven, too. But it's on the large side for a single stack. About 1.2" wide at the grip.
The thinnest 1911-style 9mm is the Springfield EMP, which is about 1.1" thick in the grip I think.
The new Kahr P380 measures less than .75" thick at the thickest part of the grip. But it's a .380. And those will probably be hard to find for a while until they are out for a while.
I've thought a lot about the Kahr PM and MK 9 and 40. I've never shot one. I've heard both good and bad things about them, with the majority been positive. If I ever get my hands on a PM9 to shoot and it proves reliable for me, I'd consider picking one up. They are in the same size league as the Ruger, Seecamp, Kel-Tec, etc. mouse guns.
Anyway, hope some of that helps or gives you some stuff to research. Kahr PM9, Walther PPS, Rohrbaugh R9, Springfield EMP, Sig 239, Kel-Tec PF-9. Start there.