^^^this^^^.....works nicely, best wick available, and CHEAP...!Use much more than you would cotton.
Cut the length you want and peel away ~1/2 for a 3mm coil and ~1/3 for 2.5mm coils.
Twist it, not super tight but twisted a bit to help you feed it through the coil. Once in the coil, untwist it and slide it back & forth a bit, there should be more tension than you're used to feeling feeding a cotton wick through.
Cotton expands, rayon contracts so you have to use more than you would with cotton.