i am looking at getting this bunk bed www.bedkingdom.co.uk/parisot-tam-tam-bunk-bed-pine.html for my boys. but when i rang up about it the person said that they come up a bit bigger then the standard single so will be 10cm longer in length. he said that some people will get the normal standard single matteress & just have the gap, has anyone done this before? thanx