I suggest taking 1 level of "monk" but use different flavour text to describe him.
He hasn't had any monastic training at all, but a lifetime of brawling has made him deadly with his fists. His stunning headbutt is feared in bars up and down the land. Ditch the monk weapons, and he can wear armour happily (not worrying about WIS ac bonus or the 'monk' abilities which he then doesn't get access too).
This gives him good saves, good access to some important skills from 1st level, base 1d6 damage unarmed and grappling which doesn't provoke an AoO and can be used for nonlethal or lethal attacks.
Then just take the rest of his levels as fighter and enjoy the fighter BAB, hp and feats to customise his unarmed brawling.
Basically the monk class *doesn't* have to represent a monastry trained ascetic - certainly at 1st level it is a package of skills and abilities which can be described in a completely different way - the pugilist.
Cheers