Too strong, but something that merged the War Domain or Gloomstalker ability might be possible.
* Combat Rush - If you take the Attack action on your first turn in combat, you can make one additional weapon attack as a bonus action that turn. You can use this ability a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
Alternatively, something that limits the bonus attacks to when you miss, but features a
* Feinting Style - When you make an attack as part of the Attack action on your turn and you miss on an attack, you can make one additional weapon attack as a bonus action that turn. You can use this ability a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.