I chose the XL diaper cover to use over regular folding diapers. It is a little loose yet, since the child weighs only 9 kilos, but I found the OS cover too small for the folding diaper (Pupus 80x80). At least I will be able to use this cover for a long time.
When at home, a folding diaper and a cover is very economical for the wash, because you can change the inner diaper a few times in the same cover before washing. But for the daycare, I use pockets.