Aubameyang is a good option,but has lost his touch,has good pace which could be very vital against defense.
Xavi will get the team in a good shape, I am certain Barcelona will be in the first four soon.
An upgrade in the defense would do.
Cavani would be a great addition for 1.5 years. He doesn't want big salary and he still has ability to score goals. Agüero was a big loss to all football fans but health comes first. Aubameyang must be expensive so Barca's first target is Cavani logically.
If they sell Umtiti, Coutinho and Dest they can make a space for Cavani and if possible, Ferran Torres. That would be the biggest transfer they can do.
Actually, I think this is quite reasonable because Ansu Fati's condition has slowly worsened and Martin has also begun to slowly recover from his injury, so adding Cavani there will only increase spending money and make strikers in Barcelona more and more and the competition becomes tougher for starting line up