Definitely size up! I am usually a Medium, but purchased a Large, and it's still running small on me. I purchased 4 different bikinis, and all of them are running small and are tighter than I'd like.
The fact that the bikins are imported from Canada, and I had to pay duty was a bit offputting at first.
But overall the bikins are beautiful, I just wish they did not run so small.
I also wish you guys showed the bikinis on different types of body shapes, rather than just skinny models.