welcome! How kind of your friend to give you all those nappies!! I dont use pockets but there are planty would do and will help I think Larges would probably be good
and welcome to the Tree. I use pockets a lot with my DS. He's 22lbs and wears larges with no problem. My main pockets are Bumgenius which, stuffed with their accompanying microfibre inserts, easily last 2-3 hours on my medium-heavy wetter. Other inserts that work well are a combo of bamboo and hemp (Easy Peasy hemp boosters and petite dessous bamboo supersoakrers).
Hope things get easier for you - what are you using to stuff at the moment? Have you got gaping around the legs when lo walks?
If you're short on cash and want to try out some new stuff check out the DIY thread - if you have a sewing machine nappies are pretty easy to make and you can make them out of old towels and tshirts.
Cloth nappies really are great once you figure out how to get on with them!