I'd advocate the pair, M3 & M8. Share lenses etc.
I have the M8 and M6 (mainly as the metering in the M6 is convenient to me).
M8 (even accepting amyukie's APS sensor comment) is cheap enough now, and is perfect for I/R. I'm happy. I do know of an M3 for sale though.............. Hmmmmmm........
Gary