Flash the stock Sony ROM, I did that with my Z3C. No O2 stuff and pure Sony now.
Battery is slowly dying a death on mine (barely lasting 16 hours if I'm actually using it), but got a few months until upgrade due unfortunately. Anyone got any tips or is it just put up and shut up? Not sure what to upgrade to next time around though, all new phones are ginormous thoughc ompared to this.
I'm considering switching to the S8 when it comes out. Although the contracts will no doubt be expensive.
Depends if you wanna stay android or not. The iPhone SE is about the same size. Great spec for the screen size too.
If you wanna stay android then you could consider something Chinese ?
They have a fair amount of smaller sized phones with mediocre specs.