0-3mo
Cast on 49sts and joined in the rnd (=48sts) on 4.5mm.
Used two sets of 4.5mm circular needles for ribbing.
Did k2, p1 ribbing instead of k1, p1.
Switched to two sets of 5.0mm circular needles and blue yarn after 6 rounds of ribbing. For some reason I’ve really tightened my tension on this size hat.

3-12mo
Accidentally cast on two extra sts (58+1 instead of 56+1). Didn’t notice until I got to the decrease rnds, so had to do some fudging.
Used a 4.5mm 16” circular and a 5.0mm 16” circular until the decreases. I think the last rnd of K could be left out. (Ie for from k1, k2tog around to K2tog round).