If you would like a more practical way of protecting it, here is one for you.
TUDIA Ultra Slim Full-Matte ARCH TPU Bumper Protective Case for Sony Xperia Z5 Premium
This case is very protective and it looks great. I think that the Xperia Z5 doesn't look bulky at all when it is inside the Tudia case but it is still well protected so this one is a great choice. Its has a very unique and original design which defers it from other cases and it is made especially for Sony Xperia Z5 Premium (note that it will not fir the Xperia Z5 ) the design allows easy access to all buttons, controls and ports without having to remove the case.