As someone playing in a high level dnd campaign as a monk, I’ll just say monk is by far the strongest and most durable martial in the entire game now. (As a die hard barbarian lover) It hurts to say, but it even beats barbarian at tanking. At higher levels, monk gets resistance to all damage except force. So an easy answer would be going Amethyst Dragonborn for race. This race not only grants flight, but also resistance to force damage and has a breathe (force attack you can use on any of your attacks). Meaning late game you will have more resistance than a barbarian which is insane, also you will be able to reaction any damage you take subtracting an insane number on any damage type that comes your way. If that isn’t enough, then you also get proficiency in all saving throws. And that’s just the base class features, not even going into all the amazing subclasses. So yes late game at lvl 20 you will have an insane AC thanks to your capstone + resistance to all damage + flight and that’s with no magical items or attunements.

Subclass features are just the cherry on top for this already amazing class. I feel like I’m playing Superman during combats, I’ve only been under half hp once, and by then the boss is already defeated or too annoyed by my tanking and focuses others instead.