I am 5'7"/130lbs and regularly carry my 9mm Glock 26 with the standard 10-round magazine and a spare 17-round magazine. I also have a 9mm Glock 19, which I don't carry at the moment (as it is permanently setup for home defense). However, I easily could carry it. When hiking, I carry a 10mm Glock 20 with two spare 15-round magazines. When jogging, I carry a .380 ACP Taurus TCP 738. I always carry 4-o'clock IWB. I always carry guns with a consistent manual of arms (i.e., no manual safety, one round in the chamber, no single-action).
As already mentioned, carry a gun that you shoot well and that you would practice with often. A mouse/pocket gun may conceal easily, but will you shoot 100 rounds through it in a practice session without complaining about the recoil and can you actually hit anything with it in a real defense scenario (e.g. shooting one-handed)?
When it comes to concealing, the length of the grip is often the deciding factor as the grip often points slightly away from the body (for IWB and OWB carry) and prints into your cover garment. Width is rarely a factor. Note that as long as printing is not against the law in your state, it doesn't really matter much. Most people are completely oblivious to printing. As long as you don't wear a body-tight shirt as cover garment, you should be fine.
When it comes to comfort of carry, don't underestimate the impact of a proper holster and belt. Both help distributing the weight of the gun and keeping it close to the body. Keeping the gun close to the body also helps with concealment.
Note that if you go for the Glock 19 and it turns out to be too big for you, you can switch to the Glock 26 without necessarily replacing your holster. The Glock 26, 27, 19, 23, 17 and 22 all are based on the same frame. They only differ in frame/slide length and grip length. Holsters for larger Glocks typically accommodate the smaller ones.
Good double-stack 9mm options are the Glock 19 and 26, as well as, the S&W M&P 9c. The Springfield XD® Mod.2™ is an interesting option as well. Similar variants exist in .40 S&W.
Good single-stack 9mm options are the S&W M&P Shield without thumb safety and the Springfield XDS. Glock still refuses to make a single-stack 9mm, despite the demand for it. The S&W M&P Shield also exists in .40 S&W.