You cat use any yarn you like that matches the recommended knitting gauge. About 100 grams 200 meters even less will be enough. I had bobbin yarn. Unfortunately, I don’t remember the brand. Choose a wool that is nice to the sensitive areas of the body. Merino is fine.
Needles: 5.00 mm circular needles 20cm cord to make 40cm / 16’’ IC needle or 29cm to make 50cm/ 20’’ IC needle.
3.00 mm double pointed needles (two of them) to knit an i-cord.
Crochet hook: 4.5 mm for provisional cast on and some additional yarn.
Gauge: 10x10 cm 16 st x 24 rows
The size of the finished buff after washing 26x28 cm.
Also scissors and wool needle to hide the ends and pull the cord.