we've been using in-ear monitors for years - single ear piece - so I can hear "live" as well!
UHF sets are all the rage..... and expensive except...... ours, which work on the legal (here in UK)channel cost in the region of £35!!! - consist of a transmitter that plugs into the phono output of the desk, a belt pack receiver with a 3.5mm output jack and a pair of stereo earphones (although I use them with a mono set).
they've been great - especially when playing in larger line ups.
and as a mater of interest they work on the same frequecies as the o/b headset used by the BBC and we have used ours on several occasions with them (in stereo mode) to be aware of the on going live conversation and also the "talk Back" from the studio - of course you could also have a similar system with your sound man with the mix in one ear and him giving you prompts in the other!!!!! now how does that next verse go???
and here's the model number GPR 9000RF not sure if this model is still available but a unit much the same is from a wholesaler in Preston Lanc's UK.
good luck Pete