I need a superstretchy bind off for the neck of my sweater. I am already working in K2P2 rib on size 19 needles. Bound off once and it was too tight. I don't have bigger needles so I can't go that route.
There are several types of stretchy bind-off methods described here: http://weebleknits.blogspot.com/2003/05/stretchy-bind-offs.html
(I use the first one a lot. It's nice.)
For maximum control of the tension of your bound off edge, I think nothing beats E. Zimmerman's Sewn Bind Off.
It's like the outline stitch of embroidery origin. You can do it in a contrasting yarn if you like.
I don't know what it's called but you knit two and then knit back through the two stitches on your right needle. I think it's super stretchy
google 'suspended bind-off'. i think you'll be happy with that.