If you carry IWB, the pant fit is the most important thing. Upsizing one size will work with most guns, and once the holster is properly attached you can hide it very easily with an untucked shirt. Also, select shirts designed to be worn untucked. An untucked dress shirt draws more attention than a bold colored straight hemmed shirt.
I carry a 5" 1911 IWB, and I can hide it with t-shirts. The better the quality the less printing, but outside of friends that know I carry and one touchy waitress that I discussed earlier I am unaware of anyone knowing what I had.
For dress slacks I like my Uncle Mikes IWB clipped on the medial shank of my weak side boot. In this holster I carry my little J frame. The key is that the pant legs must be loose enough to raise in a hurry for the access ... blue jeans won't work, but my dress slacks and suits are perfect for this.