i also built a mono blue mill, although mine is not strictly M13. I run 2 Gitaxian Probes for Foresight and draw power, and some Thought Scours for mill and draw at instant speed. I concur that you should drop a few Sleeps. Also, Redirect is a great way to turn an opponent's kill or burn on themselves. and if youre willing to make a few non-M13 exceptions, Vapor Snags over Unsummons.
also, Snapcasters and Mindshriekers work well.