Pact-making 101: A guide to the 5th edition Warlock

[Shadow]

But quarterstaffs can't be used for monk-granted bonus action attacks. Only unarmed strikes are valid. So you're taking 12 levels of warlock for +CHA on only two attacks, which seems questionable.

That's where PM comes in.
Prior to lock12 you have martial arts for a bonus attack. Once you hit lock12 you can take PM and get 1d8+d+c +1d8+d+c +1d4+d+c (ord6 if your DM rules that martial arts damage applies to that attack). OA attack on entering becomes an added bonus at another 1d8+d+c.