I think the whole "big lads at the back" type is a bit old skool now. Referencing
this, there's not many truly tall forwards that play up front these days (okay that is a year or two out of date). The modern CB is fast and good with the ball. If you keep the ball you're really only defending counter attacks (i.e. pacey forwards!). Look at Toney, Armstrong, Pukki last year. Top three Championship scorers by a mile and all 1.8m (5ft 9) or below. Only Kiefer Moore or Lucas Joao (4th and 5th top Champ scorers) would worry me from a height perspective.
If we're playing a possession based game (which it appears we will based on player interviews from Spain), a no-nonsense centre back is going to f*ck everything right up. Nothing annoys me off more than when a striker thinks about a press and a CB hoofs it clear. Reason Maguire and Stones are so well thought of is because they can play with the ball. We could offset this with a decent DM who receives the ball from them but you do become very reliant or exposed if they're injured or man-marked.
In summary. I have no f*cking idea who we should sign at the back.