I have given that some consideration, 18 is one of the approved fitments. I'm not on RFTs, I have a wheelbarrow job in case of a puncture.Drop down to 18" alloys & tyres then...
Lots of folk drop a size for better ride & comfort... If you've got RFTs too, consider binning them and going to non RFTs and have a decent tyre repair kit in the boot etc...
We're about to get a new car that's on 19s; I'll be sorting a set of straight 18x8 alloys for winter tyres ASAP and the staggered 19s I may sell on and get a set of staggered 18s for summer tyres.
All will be on RFTs