I loved this classic bomber jacket online and in the brochure sent to my house, so i was thrilled to see it in my local retailer store. i anticipated that i would need a large, but i was wrong. the m fits perfectly! 
fyi: 36c, broad shoulders/back, short waist, size 10/12 in button-up or fitted tops,and dresses (usually 10) and a m in a loose-fit or knit top.
the m fits me just like the model in the photo, so i would think that you are between sizes like i usually am, you should size down. the z