Crochet steek, the way to go, me thinks.
Be sure to use wool, not some funny blends. Here I have Blue faced DK and the brown contrast steek yarn is Shetland. Please don’t use bamboo or similar slippery stuff.
So, you crochet a simple chain, up and down around the center steek stitch, where the cardigan opening ought to be. There’s a pretty neat explanation here. Really quite simple and it holds together amazingly well, no unravelling whatsoever.
I did a pretty deep steek, 12 stitches (in fact, I did an uneven steek, one side has 5.5 and the other 6.5 stitches, as it worked better with the pattern as I just left out one 12 st. cable in the center)
Now, just the borders to do, yay!