You're Coming With Me
You know better than to let your opponents get away. At 3rd level, when you land an unarmed attack you can spend your Bonus Action and one Combo Die to perform the grapple action. When you would do so roll the combo die and add the result to your check. Additionally you can grapple creatures of any size.
Suplex, Lock, and Throw
You're accustomed to fighting enemies close up and personal. At 10th level when you're grappling an enemy you can perform one of the following actions in place of an unarmed weapon attack on your turn.
Suplex: You can attempt to slam the enemy into the ground. The grappled creature must make a Strength Save versus your Brawl Save DC or take your twice your unarmed damage and be knocked prone. As a part of this attack you can spend any number of combo die increasing the Save DC by one for every two die spent.
Lock: You firm your grasp on the enemy and put them into a lethal lock. The grappled creature must make a Dexterity Save versus your Brawl Save DC or become restrained. Additionally at the start of the enemies turn they take 1d4 Bludgeoning Damage if they are still restrained in this way. This damage increases by 1d4 for each turn they are grappled to a maximum equal to your proficiency bonus. When the creature attempts or reattempts this save you can spend two combo die to increase the Save DC by one.
Throw: You attempt to toss the grappled creature aside. The grappled creature must make a Strength Save versus your Brawl Save DC or be thrown a number of feet equal to your Strength modifier x 5 and take your unarmed damage. As a part of throwing the creature you can spend a combo die and increase the distance thrown by 5 x half the die roll (rounded up). A creature two size categories or more larger than you has advantage on the roll.
Ground Fighting
You know how to ground and pound. At 14th level you do not suffer from disadvantage when making unarmed attacks while prone. Additionally when you are grappling a proned creature you deal an additional die of damage with unarmed or brawler weapon attacks and techniques.
Meat Shield
Why take damage when you have a nearby body to take it for you? At 18th level if you would take damage while grappling a creature you can use your reaction to split half of that damage (rounded up) to your grappled target.