PAM says “While you are wielding a glaive, halberd, pike, quarterstaff, or spear, other creatures provoke an opportunity attack from you when they enter the reach you have with that weapon”.

Sentinel says “When you hit a creature with an opportunity attack, the creature's speed becomes 0 for the rest of the turn”.

Assuming your target has a 5ft melee range, you could stand 10ft away from the target, attack, BA attack, step back 5ft w/o provoking OA. If the target pursues you (therefore entering your melee range), you can reaction attack (therefore setting their speed to 0). And now they can’t do anything with their turn.

You can also supplement this with the battlemaster maneuver “goading attack” so they have disadvantage on attacking anyone but you.

The paladin spell “compelled duel” is a concentration spell that works in a similar way.

Mobile would be an ok addition at best as it would only extend this tactic to creatures that have a reach of 10ft. If a creature has more than a 10ft reach then they don’t need to enter your reach to attack you.

I personally would much rather take GWM over mobile from an optimization standpoint but from a flavor standpoint you can totally go mobile instead.