I can't really speak for the N frame, but the smallest grips I've seen for my K frames are the Pachmayr Compac Professional Grips. If they make them for the N frame that might be the ticket. The newer ones have some fit and finish issues, IMO. So maybe search for an older set.
Uncle Mikes boot grips for the K frame are really nice and compact. Not sure if they were ever made for the N frame. Unfortunately discontinued, so they would have to be searched for.
I have tried the Hogue Bantam rubber grips (K/L frame ~ #62000), that snap on the grip frame, on my N frame rb. They feel great, even though they don't match the rear of the grip frame. Now I just have to wait until they make an N frame version.