Hi, I'm looking to buy the Genesee Men's Waterproof Parka Jacket, but I don't know which size to buy and my local stores don't stock them. I need either Small or Medium. My waist size is 81cm. Looking at their size guide I think I need Medium as Small might just be too tight. But reading comments on other Trespass Jackets, it seems their Jackets might be bigger than what the size guide indicates. Can anyone who has bought size Small advise if they found it bigger than expected? My other worry is Medium might be too big. I contacted their customer support but they said they can't advise as it's "personal preference" regarding size Thanks!