I went to the Mazda dealer and they had pads on the shelf that were the correct size - both OEM and Mintex branded (£95 and £50 respectively). So I took the Mintex and all is well.
So just for anyone who is looking to buy rear pads, on my car (your's may vary...) which is a 2017 registered 2016 model CX5 175 Diesel Sport Nav, EuroCarparts, AutoDoc, etc list rear pads that did not fit. They all seem to suggest the pads are 112mm. Mine are 117mm.
I am returning a set of Bosch 0 986 494 732 and have fitted Mintex MDB3866 Both packs indicate they fit the rear axle of the CX5 - but they are a different physical size. The Mintex being 117mm long, and the Bosch 112mm.