Stephen has the 275/40R18 on his car, I'm thinking that he just made a mistype with the 45. The options for larger staggered tire sizes in 18" are diminishing, the only ones in the 255/45 & 285/40R18 combo I'd currently recommend are the latest from Continental, the ExtremeContact Sport. Very nice street tire with good dry & wet grip, and could be used for autocross or track days … bearing in mind that you won't keep up with people that are running the max effort stuff like the RE-71R.
https://www.continentaltire.ca/car/t...econtact-sport
Another option for staggered is to go with 245/45R18 and 275/40R18. Still not ideal, but better than your OEM 235 tires. Those sizes are much more common, and give you many more choices for brand and model. An excellent option at a great price is the Firestone Firehawk Indy 500, which are made from the same carcass as a Bridgestone RE003, one of their tires not sold in North America. These are impressive performers, especially when the price is factored in.
https://www.firestonetire.ca/tire/firehawk-indy-500
Wheel sizes needed would be 18x9 with offset in the +35 range, and 18x10 with offset in the +40 range, give or take a few mm either way. If doing the 275/40R18 all around, then you should have 9.5" or 10" wheels with offset in the +40 to +45 range.