As far as a larger gun being concealable, it can be done with the right holster and clothing. I can and often do carry a Beretta 92 - not exactly a pocket gun, but has 18+1 of 9mm. But finding the right holster and a good gun belt can run another $150+ easily. But if I had to keep only one handgun it would be my 642 just because it is so much more concealable in all situations.
IF you can swing another $100 or so, you can pick up a S&W j-frame. There are 2 in the classifieds here - a 442 and a 37-2.
TITCR
I would suggest a 642 or a 442. Or an all stainless S&W J frame.
For more money - I would look at compact 9mms. Glock, S&W, Springfield, Walther, SIG, HK, etc.