For me it's got to be versatile - a preferably ball-playing CB who can also move up into DM if needed. He can slot in for Durante, and Ridenton if needed. Someone like Jan Kirchhoff would be good if we got a Chinese takeover tonight (although it might not be completely off the cards - he's in dogshark form and we've seen stranger things).
Someone realistic and would fix the problems is Emir Spahic - a Bosnian legend (same nationality as Darije), who although he is old as time, has been footing it regularly in the Bundesliga, La Liga, and Ligue 1 for the past decade or so without any fitness issues.