How to do a very stretchy cast-off

I’m making a shrug to my own pattern.

I cast on 40 stitches with the long tail method of casting of its ‘stretchiness’. Did a 2 x 2 rib on 4mm needles for 20 rows, then changed to 7mm needles for stocking stitch, increasing by 2 stitches in every second row until I got 80 stitches. Knitted those 80 stitches in stocking stitch for 50 cm, and then decreased 2 stitches in every second row until back down to 40 stitches and then back with the 4mm needles and the 2 x 2 rib again. I tried the only cast-off I know, which is the basic knit bind-off, but its far too tight and means the rib isn’t stretchy, which its supposed to be. The long-tail cast on side is just fine.

Any ideas on how to make the cast off as stretchy as the cast-on?

I can’t remember the website but this is supposed to be the “stretchiest”

K1, *yo, k1, lift the first k1 and the yo together, pass them over the second k1 and off the needle; repeat from * across. You will have 1 st left on the right needle. Yo, knit into the very first cast off stitch, leaving a 6-8" tail, clip the yarn and pull through the yo and the last stitch, weave in end. Hope this helps…

I DID find the website in case my instructions are lacking:Jeny’s suprisingly stretchy bind off