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I used cloth diapers for both mine (one boy, one girl) , so this advice is from that experience.
1) when they were small (newborn-1 month ca) I used large muslin squares instead of regular diapers which were too bulky. (muslin=British term, closest American term is soft cotton like double gauze. Here's where I got mine and I highly recommend them: https://www.johnlewis.com/john-lewis...ite/p230650111). You fold the muslin to fit the baby perfectly, and I used nappy nippers to close them. 2) When they were older I used waterproof covers with either shaped nappies (my first) or terry towels (my second). By terry towels I mean a terrycloth towel about 20" square, but the terrycloth isn't quite as thick as a regular towel. Still, think about a large sort of thin washcloth and you have the general idea.
Why did I like muslins and terry towels better than shaped nappies? because they were a) more versatile; b) much easier to clean; and c) much easier to dry. I washed them very hot and we still use the terry towels for wiping up spills (or mopping the bed after wetting which thankfully is hardly ever any more).
I made myself a nappy carrier the size of a large stuff sack for the terry towels, which I folded before I put in, and a large washable PU sack for the dirties.. I also had a supply of washcloths that I had cut into four pieces each and a screw top jar full of water with a drop or two of tea tree oil to use for wipes (just throw them in with the dirty nappies). I kept the wipes/water/ointment in a separate small container in the larger nappy stuff sack, which also held the dirties bag folded before there were dirties in it.
I reckon all this stuff could fit in the bottom pocket of the S25, leaving the top free for clothes, snacks, and toys. Organisation is key because otherwise you will forget clothes, snacks, toys, wipes, nappies, and/or dirty bag, ask me how I know. For this reason I also had an emergency pack with a couple of extra disposables and a tiny pack of disposable wipes. That just lived in my purse.
PS here's a UK-based resource that I used https://www.thenappylady.co.uk/flat-...y-squares.html