I'm online shopping at Dorothy Perkins. Was in the shop the other day and in leggings I take a size 14 but in skinny jeans took an 18 although the waist gaps hugely and requires a belt, I couldnt quite do the button up on the 16's. So online, I'm looking at the reduced stuff and there are some grey treggings and I dont know if I should try a 16 or 14 or what?