I bought an Incognito Mini, with extra divider, so there's three padded compartments. It fits my Zeiss Ikon ZI, two lens kit, light meter, filters, film, etc. The bag is one of the smallest I could find, but still fit my gear. I'm not sure how big your FM2n is but it might fit your needs. They have larger bags as well.

http://www.courierwareusa.com/