I'm looking at the dr martens vegan cherry red Chelsea boots. https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F283736690387 What's the sizing like? I'm a 4 but wondering if I should get a 5 . Anyone any thoughts? Thanks