There is a free pattern for a similar coat on burdastyle: http://www.burdastyle.com/patterns/talea
The seaming might be a bit more difficult on this style, but if you have some experience with princess seams, it shouldn't be beyond your capabilities.
The reason why many coats have back yokes is to follow the contours of the body. Coats are usually made of heavier material and thus need to have a good fit around the shoulders and upper back. People's shoulders have a natural curve (some more than others) and the yoke allows more shaping across that horizontal seam. Some coats solve the problem with long princess seams that fall from the shoulders or with unique shoulder pattern pieces or with plain darts.
If you changed the pattern to having just one back piece, the resulting coat would fit differently, so it might be better just to start with a different pattern. Most patterns you will find will have at least the amount of complexity of the one you posted, so if you want something simpler, I suggest that you start with a cape pattern.