It's probably better to be honest and admit I haven't researched this subject at all, but knowledge gathered here is distilled wisdom and experience, and much more use than blundering round the internet looking for something I don't even know the name of.

I'll also admit to being everyone's nightmare, a semi-deaf accordionist! I only have one operational ear, having dropped myself on the head as a youngster, and I can't hear diddly coming though the monitor until either the feedback starts howling, or fellow musicians' ears bleed. This leads to erring on the side of caution whilst playing, which leads to just chord vamping.

Is there an ear-piece monitor on the market that can play back my own instrument? I do occasionally use my small Behringer mixer desk, prior to feeding the PA desk, so presumably I can pull my own sound off there. I've also already got a wireless transmitter for untethered instrumental use, if that makes any difference.