I've got a Acer Predator 27" xb271hu, but that might be a little overkill depending on budget.
So personally I'd just grab a 144hz monitor with either 24" or 27" as they are often very nice.
I've got a pretty nice rig. (i7-8700, 1080ti, 16gb ram) and unless you are really struggling with the FPS there isn't really any point. Arma is stuck at a lower FPS range 😓