The lab coat is essential, although I don't care if the clothes underneath are scrubs or street casual. The old-timey doctor shirts in mitsuki's link would work, too!
The more accoutrement (stethoscope, tongue depressors, Rx pad) the better! I wouldn't even mind a surgical cap and face mask. All of those layers of clothing on the doc would underscore the difference in our positions (since I'm completely naked). It speaks to the CMNF component of this kind of play.