consider one size options. they might not fit as trim for a newborn, but by 3 months they should be fine.
i used greenkids pockets as covers. inside was a pad folded flanellette flat with microfleece on top. this meant the pocket could be used more than once like designed
i also did the same with a fleece cover which i got cheaply secondhand as i dont sew.
was very surprised to find terry flats were good
