I think getting 2 CBs will help. One to replace Puyol and one to provide depth/competition and give Pique something to think about.
Marquinhos could be perfect for this IMO, he's also young and has huge potential.
As for the starting CB, I'm not sure. Kompany's not gonna happen, but he'd definitely be my first choice if the rumors had any credibility whatsoever. Otherwise, I think Hummels would be a decent option, though his similarity to Pique could be a problem. Subotic or Vertonghen maybe?
We'll probably need to sell a few players if we want to get 2 CBs and a GK though. Then again, we can pull it off IMO by selling Valdes and loaned players (Afellay, etc). That'll give us 70m to spend (about 10m for Valdes and about another 10 for Afellay) which should be enough for a GK (~20m), Puyol replacement (25-30m) and another CB (10-20m).
As for Bartra, he should be loaned to give him more game time if we get 2 CBs, since we'll have 5 (Pique, 2 new CBs, Masch, Puyol). Then again, Puyol's injury prone and Masch isn't a true CB...