I'm not too certain, but I think that a 2.5mm ID would probably be an optimal size. But all you can do is try, let us know how it goes.
Could even probably try Rayon if the worst comes to the worst. Tidi non sterile Rayon balls are best supposedly, but never had the oppotunity to try them as I'm in the UK and Grahames Cellucotton Rayon is okay and available from a lot of places.