I used what I had in the car (needed these on a road trip), but I think any sock weight or fingering weight yarn would work. Mine was 2 ply shetland, which is a little itchy, but nice and toasty.

Ditto the needles. I think you could easily use anything up to a 3 mm. My mitts are a little tight; 2s would have been snug, 3s generous.

You will need a few yards of contrast color.