For the blue body suit its best you get your exact size, it fits much more snug than the black and it is much thinner so do be careful when putting it on if you have sharp or pointy nails! This body has buttons on the neck piece in the back for an easier way to put it on.
As for the black body suit, its much more solid/thicker in color and material and does have a bit more stretch, so if you’re a medium you can also do a small. Its ribbed so not as thin as the blue and goes over your head.
