Clothes for cloth bums

i'm a wool and flecce lady but i have normal clothes that go over my prefold now that i have found them
i find the if i buy the next size up that works but my son quite small for his age

Thanks everyone. She's inherited a lot of GAP stuff but is already out of the 12-18 stuff, which is where the inherited sizes stop! No Asda in Ireland but i keep hearing how great it is. The jeans i mentioned above are tesco & they give bad builders bum.
I love the idea of pre- loved boden & monsoon. I love their stuff & H&M too. Gotta go shopping so.
Thanks

i get stuff from frugi in the sales- just the odd thing and the rest is either made by me/ from "normal" shops. my parents mainly get things from monsoon and marks. i've had stuff from tescos or asda which is roomy. and there's always ebay/ sales boards for second hand stuff