If Luiz is a done deal, the next defenders we need a rightback and a cb/lb. I think we should go after one of Laporte, Mathieu, or Yaroslav Rakitskiy for the cb/lb player. And only God knows who we could get for rightback.
Edit: hopefully it's Laporte.
Laporte will be too expensive. Why not o after Mussachio who will be available for free? Pique/Luiz, Mussachio/Bartra.