You can always run a set of wheel spacers to push your factory rims outward in the meantime until you decide to purchase new wheels. Keep in mind that 18" rims won't really give you a whole lot of sidewall.

Also some tire companies won't touch your tire/ wheel combo with spacers installed. If you have to get a flat fixed it would be best to remove the tire for them to fix it. Call your local tire shops beforehand to confirm their protocols regarding spacers.

I would recommend a higher end spacer from a reputable manufacture for a good quality set. Don't skimp for cheap ones.