I just used Moses basket sheets in my pram. Was a godsend when she was sick or had a nappy explosion!
We used to just use a large muslin and wrap that round the pram mattress, worked a treat! Also fold a muslin around the head area so if they spit up, you aren’t having to wash the full sheet x
Our Moses basket sheets fit our pram mattress too (they are so stretchy!) ☺️ would definitely recommend getting a mattress protector for it too x