Hi Victoria - If William is a heavy wetter I would suggest using a 2 part nappy rather than one of your pockets as they might gape at the legs if you have to use lots of stuffing. Ive used boosted Little Lambs before which are very similar to your Tots Bots, and boosted inside and outside of the nappy. So, inside I would use a giant fleece liner that covers all of the inside of the nappy (if you dont have one, you could cut one up yourself from an old fleece blanket), put a mf insert under this inside the nappy, then put the nappy on. Then I would put as many layers of hemp as possible underneath, at closer to the front where he wees, and secure it with a good close fastening wrap. Wool wraps could help as they help to evaporate the wee a little bit and I find when Im using wool the nappy isnt as soggy in the morning.
Hemp inserts - as they have to be washed about 10 times before they reach their full absorbancy, you would be best trying to get a few 2nd hand so you could use them quickly - try posting a wanted ad on here, they arent easy to come by though. Easy peasy hemp boosters are fantastic and only £2 each, but they can take ages to get here, otherwise Green Acre Design Hemp are good from Babykind.co.uk, Ellas House Hemp from TwinkleontheWeb.com and Ive heard good things about Hemp Babies Bigger Weed Hemp too from WizzysWorld.com (where you get free postage). Ive had good fast delivery from all 3 of these suppliers.
I never had to boost my night notions with anything more than what came with it - fc this will solve your problems.