Ezz
My DD still wears BBB + trifold booster at night (in rotation with night nappies) and i have managed to stop the leaks

I found that i needed to make sure the wool cover (in large).. was up and against the skin of her Belly - so that NO nappy could be seen at all. She is a tummy sleep and this is causing the leaks when her clothes could come in contact with the nappy as the cover was not high enough.

I also put the bamboo trifold inside the nappy under the 2 snap in boosters and have the long booster folded in 3's at the front (again as she is a tummy sleeper).

If you find the BBH wool cover does not come up high enough to completely cover the nappy. i would suggest going for a pair of woolen longies or shorties and her BBH dont seem to leak overnight with these.

HTH