Honestly, the wheel diameter isn't the big issue, it's the width vs. offset. Even an 18" wheel would cause complications if the offset was wrong. Most Mercedes-compatible wheels are already hub-centric, it's the spacers that can cause issues if they're not.

Factory offset is +35mm, but that's with a 7.5" wide wheel. By running an inch wider wheel, you need to push the wheel out a few mm further.

Many people on here have run a 19x8.5" front wheel with +32mm offset. Yes, even lowered folks. You will get some slight rubbing at high lock, low-speed turns but aside from that you'll be fine. +30mm would be even better for clearance, but you will stick past the fender very slightly.

I'd just buy the set of 19's, if the deal is good enough and this is a wheel you've been looking for forever. We can help you make them work.