all barca need are some players with height. the absence of Abidal hurt them in the last stages of the season. In my honest opinion, i'd want a player competing for that right wing-back position (currently occupied by alves), alves is prone to the defensive mistake and need I mention, has a horrible final cross/pass.
also, another obvious change would be in goal. It was sad watching Valdes in goal this season. Im just spitballing here, but I think he only made 3 saves in a span of 10 days (Chelsea, Real, Chelsea). Sure, Barca's play is such that Valdes never gets called upon more than a few times in a match; but I was honestly expecting him pull something like this off:
