It is your car, and feel free to do whatever you want to your car. But 19s on a G body will look silly. There will be basically rubber band sidewalls. It will ride and perform poorly.
I have 17 inch Euromiester wheels 7 & 8 width. and 225/45 front and 255/40s rear. The fill the wheel wells and look great.
Again, your car, so do whatever you want, but I suspect you will hate how it handles with 19s and rubber band sidewalls.
Good luck.