What others have said.
I would suggest that if you're uncomfortable riding with a relatively loose cinch/girth, you need to work on your balance. This is just incredibly important.
That said, roller buckles are great, and I like elastic on both sides of the girth; so does my horse :-) With our western/endurance saddle we use a slightly stretchy mohair cinch, with a roller buckle, but even so, I never tighten it more than snug. I like to be able to fit my fingers between the cinch and horse.
Georgie T. is as round as a barrel, with no withers at all, and no amount of "tight" will keep his custom-made-for-him Synergist saddle from moving sideways; I absolutely _have_ to use a step-up to get on. We ride in all kinds of technical terrain with a four-finger loose girth. Balance is your friend.
ByeBye! Steve and George
Steve Jernigan KG0MB
University of Colorado