So I bought myself a casual denim jacket which I like in size small, and I was thinking of buying a few more but I don't know if I should go a size up. I was considering getting myself a leather one of the exact same size too. Everything from the shoulders to the chest size [no horizontal or vertical lines on the back when I look in the mirror] to the sleeve length seems to be fine. It's just that if I bend down to tie my shoe or attempt to hug myself it feels tight at the back and horizontal lines form on the back. The material doesn't stretch or anything like a sweatshirt of the same size would, and it doesn't feel tight enough to tear or anything or even feel tight when I just stand straight. Is this a sign of a perfect fit, or a fit that is slightly too small?