I believe that the P3AT is an excellent choice for carry. I have two holsters for mine. Here are generic pics from the manufacturers.
The first one I got was a Galco holster, which are in stock at area gun stores. There is a more expensive horsehide version that you probably want to avoid as there is little benefit to it. Mine is the ordinary leather version:
The problem with the Galco, for me, is that the spring and the extra layer of leather around the top, designed for ease of reholstering, added excessively to the overall width, almost 1/4" or so. This interfered with concealment. I do not feel that tactical reholstering is a consideration when selecting a carry holster.
Another consideration with the Galco holster is that one must cultivate a style of draw that causes the holster to catch on the lip of the pocket as it grips the pistol tightly enough that they will come out together otherwise.
Then I got a Mika holster, which took some time to arrive:
Initially, I was concerned about the gun staying in the holster, but this has not been a problem even though the fit is fairly loose. I've been extremely pleased with this holster. I keep the pistol in a front jeans pocket. I find that it breaks up the outline of the pistol quite well, and it does not add much thickness.