We have a blanket on the mattress, a waterproof mattress protector, a cotton fitted sheet, a flat sheet, a polar fleece blanket and a duvet on keziah at the moment..she also has a Safe T Sleep so doesn't need to be swaddled at night but does during the day as we don't use it
We also have a 100% cotton Air Cell blanket that we used in the summer time! She's a hot baby (3 degrees hotter than everyone else) and STILL got hot under that so we often just put a sheet over her until it got a little cooler
Also, like Aimee said.. use flat cotton nappies under his head just in case of spills.. it saves heaps of time