This was my first time renting from Fitzroy, and it was a very easy experience. I didn't go in store and did it all online. I just looked at the measurements of the dress and looked at the Helsi website and saw the model's measurements and that she was wearing a XS. I got the XS and it fit very well (phew!). For reference, I'm 5'3", 102 lbs, 34A. It was tight enough that it didn't slip down, I only had to readjust once or twice. Overall, a wonderful experience and I will be renting from Fitzroy ...