As others have mentioned, I too used inline skate wheels. 60 mm I think - perhaps 65 mm. My goal was to get some wheels that gave me a bit more clearance when it was being wheeled around in shopping cart mode, but not so large that they struck my heels when cycling - something you might want to think about. (I'm 5'11"; size 11 shoes for reference.)
The bike folds fine, and still packs down into my hardcase no problem. However, it is a bit more difficult to "turn" when in shopping cart mode.
(Arghh... sorry, it's upside down for some reason... don't know why...)