Someone gave me a really nice quality, but damaged plain white super king size duvet cover. Not usable as a duvet cover anymore because of 2 rips and damaged poppers it was lovely plain white cotton, smooth and very fine.
I chose this size as it is also used by Ikea for their GOSA ASTER Pillow. so I can purchase covers, buy other pillows the same size etc if required. It is a fantastic size.