There is mixed feedback about the sizing of this garment.
I'm 5'9, my waist is 31". Im a slim/medium build.
I have looked at the sizing guide which would put me in a Small... but everyone says buy a size up, should I go for Medium?
Go for a medium!! I am 5'10", 12 stone, 32" waist and average build. I needed a large., having originally ordered a medium! Hope that helps!!