Without seeing a picture of exactly what's going on on the back of your coat, it's tough to diagnose the issue, as it could be any number of things. Darts should work, as long as the darts are at their widest (taking in the most material) where you are narrowest (at the waist).
Anyway, the major pattern manufacturers all have their catalogs available to browse online - Simplicity, McCall's, Butterick, and Vogue.
Pictures and tutorials from my costuming portfolio at Syagria's Cosplay Site!
Star Trek Original Series Uniform!
Original Creation for AB13
Most Recent Con:
PAX East, Anime Boston 2013