I live in the tropics so I know how you feel about warm weather carry. I like to carry IWB at 0400 in a Highnoon holster (Downunder or Public Secret model, check High Noon Holsters
). Having the right shirt is the key. If you are informal an extra-size t-shirt works well, otherwise a polo or golf type shirt or Hawaiian print type shirt works well. A Glock 19 should conceal pretty well ( I have one also). And last but not least there is always the waist pack option if you live in an area where it will blend in (check out the pistol packs at Concealment Shooting Equipment Handgun Gun Cases
. The darker colored nylon packs work well). Good luck in your search.
best wishes- oldandslow