Hey this is a common topic with CCW. I have found people who carry all but religiously 9 months out of the year then hide a gun in their car during summer months because of the temp and humidity and of course the lighter, shorter clothing.
(Ahem) it's one of the things I actually like about summer! (Nuff said)
So for Spring to Summer carry (55-80 degrees) with a t-shirt and untucked lightweight unbuttoned cotton over -shirt I depend on IWB holsters such as my Milt Sparks/Bruce Nelson Summer Special. For a Commander sized 1911 it can't be beat. Or even one of the new broad rear panel inside the pants holsters work and there are dozens now to try. I prefer the Bianchi Model 135 but there are many in leather and Kydex.
Speaking of Kydex either IWB or a belt slide I've been impressed with Leadfarmers Inc holsters, but likely you can find a local guy or gal making them in the $45-65 range. Make sure your belt works with it though.
Now it's over 80 degrees and it's no longer "over shirt" weather but "under your polo or t-shirt" weather.
I use a Bianchi, Galco King Tuk, or DeSantis pocket holster with my M&P Shield or S&W 442 revolver. I am also a fan of the Galco JAK holster that's inside the belt but outside the pants. Very good with the Shield or my M&P 40c or even Glock 27. I have one for my Ed Brown Special Forces when I have a long dark colored polo on.
I am NOT a fan of appendix IWB carry that is popular with KelTec shooters using the 'clip draw' clip. Maybe 5:00 (for right hander's) hip carry but I stay away from appendix carry (12-2:00 right hand side).
Lastly there's the Belly bands and they work. I know female detectives, undercover, and body guards who swear by them for women. Under a loose shirt that can be pulled up quickly they work for everyone. I also have a 5.11 summer concealment shirt that looks like a short sleeved untucked button up casual shirt. It has a combination of Velcro and snaps replacing the normal buttons for "pull up or tear-away" access to your rig.
Ok, these some ideas....anybody else?