Adept | Level Up This is what the Adept class from Level Up has to offer. Does it come close to what you want to see for the Monk in One D&D?
curious
I dislike its name, the exertion mechanic, the fact it leans harder toward “martial arts expert” and away from “mystic warrior”, etc. tbh I mostly just am not into the general style and vibe of A5e, is probably the real issue.
That all said, if you took that and made it more mystical, and kept the brawlers and other non-mystic types in the fighter and Barbarian (there really should be a bareknuckle brawler Barbarian, anyway), maybe even put the kensei type into the rogue, and just go all in on “this is a warrior from an esoteric/mystical school” and lean into the actual point of ki in martial arts, which is that all movement and action is rooted in your breath, regardless of whether you’re a fighter, athlete, singer, or whatever else, it’s not a bad start.
Which is why my mystic has focus dice (combined martial arts die and ki points), with the flavor of focus being centered on your breath, and you have techniques ranging from manuevers to stances to meditations, and then “regimens” which are class features you choose during a long rest, activating a small number from a larger pool that you know.
Also, for me, the archetype begs to be able to go to a master of a school and learn a new technique, like a wizard learning a new spell, so techniques and regimens both work that way, with a limit to how many you have prepared via conditioning and focusing on certain aspects of training.