I find hemp or microfibre to be the best for boosting.
I would look at getting another night nappy Kelly - maybe try a VBSN or try a Poochie from Naturally Mum. I was a tester for these, and they are great. Very absorbant, although they take a while to dry. The booster snaps on to the outside of the nappy, so it doesn't change the fit of the nappy.
The other thing to try is woollen soakers at night time as they will absorb alot of wee overnight - without leaking through. As long asyou get a night time weighted wool.