Prefolds and a cover?

There are some that make tiny nappies like totsbots teenyfits, kissaluvs NB, happy heiny micro premmie,, bubblebubs make a tiny AI2 I think too.
I have both the totsbots teenyfits and the kissaluvs newborns for DD3 and they would swim on your friend's bub. My girl was born 3.9kgs and if anything they were a little big for her around the thighs at the start