I tried making some out of stretch terry. I thought about the fit too. It was hard to find stretch terry that had a high enough % of cotton to be absorbant enough. Maybe stretch hemp something would work better. I am using stretchy hemp sherpa prefolds and jersey flats that Corey at Doodlebottoms made. The flats fit great! (let you know about the sherpa later, just got them today...
I made non-stretch terry rectangle flat diapers out of the cute colorful 100% cotton towels that are on sale her at Walmart for $2.50 each (can make 2-3 diapers per towel). Made them 15x18, serged the edges, and sewed a matching washcloth in the center so it opens trifold like a burrito to wash or stuff (like the eezi-gear eezi-folds open). Darn if they aren't cute! I can snappi them too. When the diaper's on, the soaker has four layers of terry. The body only has one, so it's not bulky at all.