Purchased M38 size. I am 36 C bust with wide shoulders & long arms. The blouse fits nicely and is really elegant. The discomfort comes in where the interior stitches are on the sleeves. The scratchy seem work is the only thing detracting this from 5 stars.
I adore this shirt! I'd say it breathes pretty well and it is amazingly comfortable. I am a 36D-30-40 and I bought the large. It fits my average shoulders and gives a fairly functional range of motion. It also compliments my waist without hugging it uncomfortably. The flare at the bottom gives comfortable room for my hips. It looks great with an under or over-bust corset, with jeans/slacks, high-waisted skirt, and with or without the scarf. My only note for future buyers: A soft or sports bra is required if I don't want to strain the button across the bust. For a regular bra, I'd need the XL. If you're unsure or just want to be safe, I'd suggest going the next size up on the chart to allow room in the chest area.