If we are going to play a City-style 3 man midfield, we are going to have to buy. It's not just about having 3 men in midfield. The front two players in that 3 need to be able to pass the ball and move well on offense; and if we lose the ball, have the energy to quickly recover it. On our team, the only person who comes close to meeting that spec is Ceballos. The other players just do not have the combination of passing and defensive game to make it happen.
So ideally we would buy one midfielder in January who could come in and fix the problem. There are clearly players who just will not work. One is Ozil, so we shouldn't even waste time. Nelson and ESR could work but they are so raw.