Agree with the above, its all about the drawstring/waistband of the shorts, because the weight of the gun is something you cant change.
Pro-Tip - pick up a couple pairs of athletic shorts that have an actual "waistband," not just the little white string that doesn't do very much. I work out regularly and coach at a gym, so I am in gym shorts almost daily. This waistband still has a drawstring, but the actual band part makes it much easier to hold up the weight of a sidearm. The design is very similar to board shorts, if that helps you picture the ones i'm talking about.
I wear the Reebok ones, you can find them at their outlet stores in the "crossfit" section, and they are usually on sell for about 20 bucks. They last forever though, ive worn the same ones for years.