I'm kind of surprised that you want to carry IWB weith warmer weather. I'm going just the opposite direction -- OWB. IWB is a sweat inducing carry method.
You never said what you're carrying, but since this is the S&W forum, I'll guess revolver. I would have said that the Galco Summer Comfort (Summer Special ripoff) was good up to the N frame size -- they're about the only maker who builds for N frames -- but they place the cylinder above the belt to avoid the 'stretch' you're going to get with the waistband of your pants. This is a bad tradeoff, in my opinion, because it puts the center of gravity above the belt since most of the mass of a concealable revolver (i.e., short barrel) is behind the barrel, so my N frame always felt like it was about to squirt out of the rig. A smaller gun, like a J frame, may not suffer from that.
For a short barrel gun, I'd go OWB, with something that has a retaining strap. Don Hume has lots of inexpensive but functional choices there, like the 721. I say this while waiting for a Milt Sparks open top PMK...