I can't think of a medieval history written by a ruler in the manner of Caesar of Churchill. Although someone else may be able to point you to something. However, there are a variety of histories written by members of the upper echelons of medieval politics writing about events of their own times. There are online editions of most of the texts I will note, though for most there are also better, more recent editions which aren't too expensive.

If you want a gossipy history from an insider, the best (broadly) medieval work that I can think of is Procopius' Secret History. Precopius was advisor to one of Emperor Justinian's key generals and wrote one of the major histories of the wars under Justinian. In his Secret History he essentially gossips about and slanders Justinian and Theodora.

As for the latin middle ages, my favourite sort of personal, dramatic history is Abelard's Historia Calamitatum. It isn't about politics, but it is an autobiography of one of the most significant scholars of the early twelfth century essentially describing all the bad things that have happened to him, mostly (so he suggests) due to everyone else being jealous of his great intellect.

For medieval politics a good place to turn would probably be Jean de Joinville's Life of Saint Louis. Joinville was a confident and advisor to King Louis IX who accompanied him on the seventh crusade, and his biography of him is somewhat more personal and conversational in tone than many medieval histories.

As to politics in the twelfth century, the two works that spring to mind are Otto of Freising's Gesta Fredrici, a biography of Emperor Frederick Barbarossa written by his uncle, and Suger of St Denis's Life of Louis the Fat, a biography of King Louis VI by probably the most important political figure in France.

As to editions, there is a good Penguin edition of Precopius, Abelard (The Letters of Abelard and Heloise, together with the rest of their letters), and Joinville (Chronicles of the Crusades, together with Geoffrey of Villehardouin's history of the fourth crusade). The translation of Otto is The Deeds of Frederick Barbarossa trans. CC Mierow and the translation of Suger is The Deeds of Louis the Fat trans. Cusimano and Moorhead. Depending where you live, you can find cheap second hand copies of the latter two online.