A few things:
- MY EDC is also a P30sk, and I'll say that it feels 'thick' to me. I'm a lean guy, so IWB isn't a challenge, but my P30sk is the most needy when it comes to positioning. When I'm just wearing shorts and a t-shirt I usually carry a Taurus G2C. Thinner and less bulky. Long way of saying you may want to look at other pistol options for IWB carry.
- Stock up on Hawaiian shirts and bowling shirts for the warm weather.
- I've seen a TON of advertisements for this 'comfort' product recently that seems designed for the issues you're facing. I've never tried it, so buyer beware: