I agree - if you can fit even a small booster (homemade or bought) in the Bubblebubs it might just be enough to help last. I love a combo of hemp, microfibre and even flannelette. Makes for a trim absorbent booster - mine were homemade though.
Otherwise you may just need to change more frequently. I generally change Thomas every 2 hrs, give or take a bit, sleep times would be the exception though.
Another option is to boost outside the nappy (so between the nappy and cover or longies). Gives extra absorption without compromising the fit of the nappy.
Good luck
