Just got my hot little hands on the Black Widow comic series from 2010. In this is a nifty lil' section called "The Black Widow Files." Like all good marketing ploys, it lists all the comics and GNs that the information is from so... *gets on Amazon and buys EVERYTHING*
As always, if MCU canon contradicts comic canon, film > comic. It's just easier that way. However I will be working in things that fit Natasha's existing profile and RP canon, (Like hardly blinking while having surgery under no anesthesia. OMFG!) and using the comics as personality and character study.