A mini mattress protector! I hadn't thought of that! We've got a standard mattress protector under our sheet and then I've been putting a big square nappy on top to catch any posits and leaking (from my boobs mainly).

How did you get a mattress protector without the fitted sides? Doesn't it make you hot? (I only say this because I lay on a sheet of plastic for a while after giving birth (I was at home), and that made me feel really hot and sticky (not breathable - obviously).