You could easily just go grab a pack of terry flats, about $20 & either make a nappy fold, or just fold it into a rectangle to lay in the nappy.
DS needs microfleece between anything & his skin, but not all babies are as sensitive as him.
Flats I find real easy as 1, you probably won't use them for long, so $20 isn't much to spend, 2, they dry so fast, 3, they can be used for a million other things. I keep one on my car seat coz its leather & gets hot, can put them in the car window for shade... I wish I'd thought of them so much earlier!

Of course Maz's night nappies are awesome & go under a cover too

What sort of cover is it? PUL, wool or fleece? PUL you might not want to use over night. Its not a great idea for long hours as its not quite as breathable as the others, but can be ok. Wool absorbs as far as I know, on top of the absorbancy of the nappy, but I've never used one. Fleece, I love...Again check out Maz's stuff

HTH