I would like a shoulder holster for my Glock 20 and am at a loss as to what to order. I have two issues. One, I would like it to ride fairly low, so it's accessible by pulling up on a sweatshirt. Two, I'm what you'd call a "large fellow", six foot and about 275 lbs.. So it needs to be big enough to fit comfortably. I guess I have three issues as I'd like to keep it under $150, which doesn't seem to be too big a deal as I've seen a lot of options in that price range. Also, do most of these shoulder rigs have the ability to swap the holster portion out so you can use it for more than one gun?