Gia Fitted Collarless Denim Vest

I'm 5'5" 125 lbs and take a small to medium size depending on the clothing. I purchased the medium but couldn't button the vest without any underlayering. To compare I also purchased the large but the armhole openings were very big and my arms are slim like in the photo. Big difference in sizing between medium and large. Must return.

This vest is stylish, thick jean material. I am between sizes of an 8to a 10. I wanted it to be more of a fitted vest so I went for a medium. It fit well, cut in on sides to show my figure, but there is a gap at the chest when buttoned up. My chest is a 37, waist 33. I'm going to size up to large. Hope the arms holes fit OK bc they are perfect for me with the medium. I usually wear an 36 D bra.