Thinking ahead

Not that I’m ready to cast off just yet (although that mini deadline is certainly approaching!) but I have been thinking about how I’m going to do it.  You see the main part of the thing is stockinette, so likely to curl without a little weight to the bottom, so I’m thinking possibly an applied i-cord cast-off.  However, part of the last row will be vertical ribbing, so needs to retain that stretchy look, which i-cord is definitely not.  Should i just gather some of the purl stitches as I’m casting off, or do something different?  At least I’ve still got a bit of time to think about it!