I have just discovered the old style mothercare brand shaped nappies fit inside the older style (the ones with the pointed tabs) Medium Fuzzis very well and make a good booster.
Mothercare don't make them anymore from what I can see but they keep cropping up on ebay every week and I have some I'm going to offer FFP when I get round to it.
I'm thinking they are a cheap option for booster as they don't sell for much even new.