Just go to halfords or some car audio shop, they all use the same single DIN cage. When you go, take your old head unit with you because depending on brand the connectors at the rear of the unit vary.
Hope this helps!
just get an aftermarket unit, if you gotta have the steering wheel controls working then just do a bit of research into what you need extra.
the originals are ok i suppose but it seemed easier and cheaper to just throw a spare one in.