Hello and welcome!
255 at the back is really too wide a tire to fit on stock rims. Not sure that you will get anything out of that size, even if it will fit without rubbing, i’m guessing that you are at stock height? It might also depend somewhat on what brand tire, as not all 255 section width tires are shaped the same. I have similar worries a about the fronts, where some have reported rubbing in that size and others not. I’ll let them chime in.
If you really want the performance gains from wider tires, then research the ideal offsets, and get a set of appropriately wider wheels. And lighter ones, as you’ll be adding a fair bit of rotating mass going to that much rubber.
If you just want to fill the fender arches better, then spacers with a tire size closer to stock would be a better option.
I’ll point you to the Alfa9 website, where Matt has the ideal tire size listed with his 4C wheel selection. You won’t likely buy there given your location, but it’s a great resource too.
Good luck!