As for sizing, I would use my high bust measurement to choose the size. Measure your chest just under the armpits and above the bust. This will give a better fit through the upper chest and shoulders. A garment like a coat generally has lots of ease. Depending on your bust measurement, you may not have to make any alterations. Generally, a full bust alteration is easier than having to alter the upper chest area which can affect the neckline, shoulder and armscye.