I have been shopping at my size for long enough to have perfected the art of walking into a straight-sized store and knowing at first glance whether or not something will stretch to fit me without looking strained. In case your eye hasn't been trained yet, I've provided some examples of non-plus size things that someone my size can probably fit. But seriously, if nothing else, remember this: elastic waistband+jersey knit=99% fail proof.
Everything below can be purchased on the Urban Outfitters website.
See the similarities between those four items? Stretch, fabric, general drapey-ness? Okay, I think you get the point. Obviously this doesn't apply to all cuts and fabrics--once you get into more structured pieces, forget about it. But when it comes to knit, at the very least, don't be afraid to try it on! You might just be surprised.