We don't need a centre half. We have two very reliable centre halves that suit the system in Otamendi and Stones (when he returns), one of the best in the world for the past decade in Vinny, who can't play every game admittedly but is an amazing third choice and a capable fourth choice in Mangala, who accepts being fourth choice, which no top centre half in Europe is going to do. We also have two up and coming prospects in Tosin and Latibeaudiere.
If we decide to sign another I'll trust in Guardiola's judgement, but we'll have a hard time convincing anyone better than Mangala to be fourth choice and we'll lose Vinny or Otamendi if we sign someone who goes ahead of them in the pecking order. We need options at pivot, left wing and left back far more than we need another centre half.