The Cotton Rich is sort of like a low pile on one side & knitt on the other, the nappy on my blog thats orange with black snaps, the one I stuffed up the snaps on is cotton rich. Its not really the same as the polar.
If the sherpa feels thinner then I was use two layers.
I would use your flannel to make fitted nappies, use it as your outter layers. You could use it for your inners but then bub would feel wet & would have to use a liner to get that dry feeling. But you could also use your Flannel as your 3rd middle layer & even make boosters out of it. I found that Isla does ok with flannel boosters if its teamed with Microfibre.

The Snaps I get from "Snaps Austraila" you need a snap press to put them on. Snaps australia supplies all of this, its not cheap to buy the press though.
Where in Sydney are you? You could always supply our snaps & have your nappies snapped for you (I'd be happy to do this for you, Im in the Hawkesbury but moving up the mountine but I am sure we could work something out if your not that far away.) I know the thing your talking about in SL, that would be better suited to thinner materials I would say.

I orginally had a free nappy pattern I found on the net but over the months I have made up my own to suit Isla better. I have found what works for her & what doesn't. I still change it around almost every other nappy I make. I also have a pattern for Covers (basically the same as my nappy pattern but larger & wider) and I am working on a newborn size atm. But I haven't got a newborn to try out the size on so I have not idea if that is going to fit lol. There are a few pg girls on BB who will probably get one to let me know how the size is.

Ask away I don't mind