Here are my suggestions...
4 regular townies - no special abilities
1 vigilante - Is a towny but gets a night kill if he wants, he doesn't have to kill if he doesn't want to since he'll want to be sure he's targetting a mafioso.
1 investigator - He gets to choose 1 player each night to learn what their role is in the game.
1 bodyguard - Similar as the doctor in that he gets to choose someone to save but if he chooses right not only does he make the save but he kills the regular mafioso.
1 Mob Boss - He is safe from the bodyguard and gets 1 chance in the game to choose someone at night and request a role/ability block on that person. If he chooses correctly and it's the bodyguard, he doesn't get to save that night....if he chooses the vigilante, he doesn't get to kill....if he chooses the investigator, he doesn't get to investigate. This is a 1 time use...not a use each night ability. Use it wisely.
1 regular mafioso - no special abilities