Well a harness could work, but really that's not something you will need because these will be so light. All you have to do is the parts that would be connected to the coat, just sew it on. There's really nothing complicated that needs a picture..I don't even know how I would make a picture to show you if needed..
Cosplay DA Regular DA
-Fate Testarossa (Mahou Shojo Lyrical Nanoha A's) ~90%-
-Ryouko Ookami (Ookami san and her 7 companions) ~75%
-Amy Sorel (Soul Calibur) 25%-