Imo the spicier build is OHMonk 9/thief rogue 3. You lose reckless attack, but with tavern brawler’s extra 5 to-hit, accuracy is already fantastic. You lose 2 damage per strike, but gain an entire extra bonus action that is resource free. That’s two more strikes with flurry of blows, an additional topple or push check, etc.

It also gives you cunning action, which is bonus action dash/disengage without costing ki. The downside is your stats are more tight, and less AC, but I was still able to get to 20 with the right gear.