n my opinion, IWB is a royal PITA...for me, it's a size larger in jeans, a larger belt...I much prefer to tailor my shirt or jacket length to prevent "printing". I've used several Galco's over the years, and found them all uncomfortable, and sweat from my upper body did no good for some of my blued-steel-beauties.
I wear my normal pant (and belt size), and find it works better than sizing up. There is initial snugness when the gun is first inserted, but the fabric quickly gives and everything feels natural and comfortable. That slight snugness really helps hold the gun/holster in place and eliminates the excess slop and holster movement you get with oversize pants.
Besides the "slop", from my experience, sizing up offers two other major negatives. One, your pants dont fit when the gun isnt present, and two, your pants look like they dont fit. The waist isnt the only thing that increases in size when you go up. Proportionally, everything looks off.
Holster wise, I had the same sweat issues as you with the Galco's, and a number of others. Comfort usually wasnt an issue as long as the holster wasnt against bare skin. If you sweat, especially if youre active, leather is a poor choice for an IWB holster. Luckily, they came up with kydex, and the problem was solved. No more rusty guns and rubbed raw skin.
My draw from an IWB also resulted in "covering" a portion of my body I'd rather not have ventilated with a 230 gr .45 slug.
Im assuming youre referring to the "appendix" position here. Not my favorite either, but more for comfort reasons than for shooting myself reasons. I suppose if you were seated it could be an issue. Then again, it can be an issue with a number of other holster choices, IWB, OWB, and a few other methods of carry. Practicing proper draw techniques pretty much eliminates the issue with any of them.