You could probably use the wool soaker.
The first night I used a Superfit Nappy cover, these are the old kind that I think they still sell at K-mart. & it's only got a central panel which is plastic backed, not sure what the rest is made from. The second night I used a Down Undie cover which is made from a PUL like material (from a kayak cover manufacturer)
You can get a thirsties cover but at $22 I couldnt' afford that at the time. This is the cover Itti Bitti recommend. I think you could use a L cover over a M Boo??? But don't quote me on that!
It would be cool it they did a see through cover so you can see the nappy underneath