A microphone or some microphones? I would try a omnidirectional microphone, where the sound does not bend around the diaphragm to avoid any sound from the back or the sides or what have you, an omni mic will pick up all sound, and you could put that a couple feet behind you, or if you can, Ideally I would just hang it really high above the piano, in front of you, after the hammers, above the harp. I would try that first, if it sounds awkward, I would just keep it somewhere on the stage. Even better, put it on a really high stand right in front of the stage, but I do not like the idea of favoring a side of the piano, even though low frequency waves are omnidirectional too, keeping the mic close to the high octaves will sound different than what you hear, so I would hang it above. I wouldn't close mic unless you will be adjusting the levels between the left channel and right channel, aka automating the levels of your right hand melody, studio cheats like that.