I have a 34 inch waist with a 44 inch chest. and my body is long. In some styles and fabrics I need a large (mostly to acommodate my chest size), but in some others I can wear a medium comfortably.
My point... with a 33 inch waist you'll probably need a medium leotard, but, depending on your other dimensions, like chest size, you may need a large.
The cotton-lycra tend to fit tighter, without as much give as say a pure nylon or a lycra-synthetic blend.
I would think that you would want a shiney-surface like lycra for your costume as Satan.
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