Sweetpea, we've been using the BumG pockets since Riv's birth, and started off using just a microfibre insert - when he got to perhaps 5 months, suddenly he increased his weeing ability and now we definitely always use 2 boosters - usually a microfibre and a bamboo or hemp. So - I'd use a microfibre (closest to his bott to quickly soak up the wee) and then a bamboo or hemp (to hold more moisture!).

All the best, they're a great nappy, sounds like you need to use more than one booster though!