Contractions aren't used in the dragon language save for one canon example from the game: "Ful, losei Dovahkiin", which means "So, you're the Dragonborn". I'm not sure how exactly "losei" is formed from the root "los" (is/are/am). It's possible "losei" could also mean "I'm", "he's/she's/it's", etc., or it may only mean "you're". We don't know for sure.

Sorry that I don't have a better answer at this time! You'd be safest not worrying about contractions. Since the goal is to shorten phrases, there'd really be no difference between "Il mii" or "Ilmii".