My first thought was Levi, but you'd make a lovely Ymir as well. I don't see a lot of Ymir cosplays, but she's a great character.
Completed Cosplays: Misty (Pokemon Indigo League), Yuki Nagato (The Melancholy of Haruhi Suzumiya), Rico (Gunslinger Girl), Yellow (Pokemon Special/Adventures), Fem!Fifth Doctor (Doctor Who)
In-Progress: Aigis (Persona 3)
Future: Alice Malvin (Pumpkin Scissors)
Future Cons: Anime Nebraskon 2013