I think it all comes down to how you feel and is it comfortable and can you breathe/move, I've recently only got my first Jersey & Shorts, I normally wear a size Large T-shirt so I thought it would be best I went into decathlon to try them on first, I'm 13.10 stone and 5'11, I felt the XL in both shorts and jersey fitted best for me, not too tight but not too loose, good fit on the shorts though. Had a look at Muddyfox gear and it seemed to be a bigger size than the decathlon stuff, a large for them for me probably so I guess it depends on the brand too.