OK, really daft question. I've just bought some Birkenstocks on line, and having arrived, they seem massive overall, but the bumps under my toes seem in about the right place. Ordered a 39 (UK6) but despite having Googled it beforehand am not sure if what I think is a 39 and what Europe is a 39 are the same thing? don't want to send them back if I've actually got the right size and they're just a bit bigger than my current sandals. Anyone know? Thanks!