Everyone’s bodies are different, to find your perfect fit, check out the Size Guide tab on the product page.
This will have the measurements for the different sizes. Match the measurements with your body's measurements and you should be all good. Need to know your measurements? Click on the full size guide link at the bottom of the size guide tab and this will show you how to measure.
It's also worth checking the product description to see what fabric is used and it's elasticity.
Still not sure? If you need it now, buy two sizes and return one for a full refund. At checkout, add your intention in the comments section and we will send out a return shipping label with the order (use the same packaging). Proceed through the returns portal here and select "Return 2nd Size Check". We will issue a full refund the instant it arrives back to us - easy.