P (watts) = I (amps) * V (volts), so you need a minimum of a 60 Watt transformer. However, the amount of power used by the machine will be determined by the machine's resistance, rather than the size of the transformer. The transformer will just determine how much power is available. You don't want to fully load your transformer (best to keep it under 80% of the rating).
I'd get a 100 or 200 Watt transformer, which will keep it under the 80% utilization recommendation.