dont use beeswax candles they have a much higher temperature and hard candles are best avoided,they have a high quantity of stearin which raises the temperature considerably, soya candles have the lowest temperature but most household candles are fine, always make sure to do a test on a less senstive area your subs skin.
ideally you want a candle with a decent width because as the wax begins to melt it forms a pool around the top of the candle giving the it time to cool slightly. On a thin candle the melted wax builds up quickly and drips off much faster.