I used at 12.75 mm needle because that is what I had.
A 15mm needle would work fine as well.

I cast off in purl because I just couldn’t rip out yet again (knit this 4 times in one evening to maximize the yarn). You could purl the second last row then cast off in knit.

It is so easy you really can knit it 4 or 5 times to get it right :)