I think Zorb II already contains bamboo... last I knew, it was basically a quilted sandwich of microfiber in between 2 layers of bamboo jersey. So it is safe to go against the skin as is.
I personally did not find it as magically absorbent as I'd hoped, but it is very trim and fast absorbing. I imagine you could do 3-4 layers and that would be plenty. I would not stitch them all together though, it would make it hard to wash clean. I would do a large piece with stitch lines to help folding, that folded up in 2-3 layers. Then you could try the overnight diaper with 1 three layer or 2 two layer inserts.
Hope that helps and good luck!