Based on your time periods, you will want to read about Middle High German (Mittelhochdeutsch), about 1000 to about 1300 CE, and then "Early New High German" (yep).

I'd first recommend German: biography of a language by Ruth Sanders (Oxford, 2010).

Secondarily, chapter 5 ("history of the language") in German: a lingustic introduction by Fagan (Cambridge, 2009); then A history of German : what the past reveals about today's language by Salmons (Oxford, 2012); or Landmarks in the history of the German language ed. Geraldine Horan, Nils Langer and Sheila Watts (Oxford 2009).

And since you seem to read German: A history of the German language through texts Young and Gloning (Routledge, 2004).