Of course we need a centre half, a new goal keeper wouldn't be a profligate outlay either, and a defensive midfield option could be more than useful too, but the thing we lack the most is a leader.
We desperately need someone who can calm things down, stop the instant sagging of spirits and make sure heads aren't lost. Someone who can quickly quell any slipping away of confidence and get things quickly sorted and stabilised when we lose a goal, so the normal avalanche doesn't get under way.
Whether that's a centre half or a midfielder, it makes no odds. It just needs to happen.