Imo we don't necesserily two new top-defenders for next season.
We have Chiellini,who I would play as CB and Criscito and Boumsong as back-ups.
Et voila':
Grygera---Milito---Chiellini---Criscito
If it doesn't work, Zebina could take Grygera's place,the same with Criscito,Molinaro...