Adapters.. but I don't recommend them, especially for just OEM wheels. You add like 20mm usually, which means you will be mounted wider with the same rim width. I recommend instead just going for 20" 5x114.3 wheels with wider width and an offset appropriate for the width. As it is now, I see sets for about $1k-1,2k used, so once you add tires, you're already closing in on the $2k mark for just OK looking wheels. Not to mention, a lot of the wheel adapters out there are cheap crap with issues like studs snapping or spinning (get trusted brands if you really want to do it still).
Now.. if you have some reaaaaaally nice wheels though.. sure.
Since you're not increasing width much or at all, I would keep it still around +55. You could probably manage further out in the 40s if you like a wider stance, but it may put more stress on the lugs, hubs, and bearings.