I would like to know the proper size for a casual dress shirt. I am wondering about a size small and a medium. I went to Jcrew today and the small gives me a better image, it doesn't look baggy and gives a very clean appearence. But I was worried about the tightness when i pull my shoulders back, the shirt is pulling on the front buttons. When i relax, they're perfectly fine. The shirt is well fit, but maybe a tight when i twist my body on purpose. I know that dress shirt shouldn't be roomy, but i would like to know the proper wear. I am worried, because I dont want to buy something and find out that i bought something too small. When i was wearing the shirt, i didn't have a undershirt on.