Hi 97 octane,
I'm 5'7", 115lbs. My favorite IWB holster is the ARG from Mitch Rosen. He made the first rear mount belt loop holster, since copied by everyone. He now has two versions, the original and thin models. If I ever buy a new one it would be the Thin model. I've been using my ARG since '94. It's for the Officers .45 ACP. It keeps the butt tucked in better than any other's I've got. BTW, it's very important to use the correct belt with any holster. The difference between close and correct, with any holster, is very noticeable.
It really helps if you start with a slim gun. You want a slim slide, slim handle(grip), and a short butt. Barrel length is least important, when the gun is carried more or less vertical, and butt length is most critical, all other dimensions being equal.
Two other holster types you might consider: Belly Band and crotch type. The Band type should have a holster pouch on the inside to cushion between you and the metal. It should be shaped to hold the gun in a proper cant for the location ie: FBI tilt for strong side, and muzzle forward for crossdraw. Drawback is increased heat retention. I know a guy who sells holsters in gun shows, he's about my size, and he will pull a long slide Glock (type C) out of his pants to demonstrate the crotch type! He carries that Glock all day, and has no problem sitting down. And he wears jeans for this! (he hates jeans-but found he had to so he could prove to customers it was possible). Heat wise, I think the crotch type would be more comfortable for you.
The belly band types I have were made by Guardian Leather, Inc. Not sure if they are still around. Excellent quality. They came in both left and right hand models. The crotch types also come in handed versions, can't remember the names.
Size comparison:
Glock 27 -------------------- Colt Officers
Slide 1.025" ---------------------- 0.920"
frame 1.150 ---------------------- 0.760
grips 1.165 ---------------------- 1.375 (custom)
height 4.00 (stock mag)---------- 4.80 (5.075 w/pad)
length 6.2 approx ----------- +0.750 longer (hammer)