you could also look at the nappy you are using for overnight.

Have a play around and see if you an find one that is more absorbant, and try using a wool cover
the wool will breathe, helping prevent nappy rash.
Do you have any other nappies?
We used a double boosted BumG pocket that worked well overnight - didnt last all night at that age, but wouldnt leak, and meant I didnt have to change her until about 4am.
You can also boost the BBH you are using to make it last longer.

Have a play and experiement a bit, look around at some other night nappies (they will be needed later on anyway)
Also keep in mind that the bamboo wont reach its max absorbancy until it has been washed and dried abut 10 times (I dont know how old your nappies are)

GL!