The whole "use the covers again" thing never works for me. Granted, mine are all double-layered covers; I don't have any of the wipe-off PUL on the inside type, which would make a big difference. I didn't buy any of the wipe-off kind because I knew I would be just putting a folded prefold down the middle and didn't want the plasticky feeling on the baby of the PUL, and because the exposed PUL didn't see too durable to me, but maybe I'm wrong on that.
All but a few of my diapers are one-size, and I found it to be a non-issue with my newborn last time. But, she was 9lb 6oz. I have a bunch of mommy's touch one size covers which I like alot. They are easy to snap to different sizes, and get teeny tiny without much bulk. I just use a prefold of the correct size under them. Sometimes instead of having the bulkiness of the snapped down size, I just snap it where I need it to be, and let there be a flap that sticks up over their belly. Didn't seem to bother dd any. The beauty of it is that a.)I can grab a diaper and know that it's going to fit my baby or my toddler, and I don't have to keep track of which diaper belongs to which kid, and b.) well, they still fit my toddler. I have all I need. I try to buy a diaper a month, or every other month, just to keep my stash going and prevent having to buy a ton when these eventually wear out. I almost always pick a one-size pocket now, and have found that the fuzzi bunz are definately the highest quality, and best fit, imo.
But, you can't beat a prefold and a cover. Simple. And, to achieve the simplicity of an aio or a pocket, I fold my covers and prefolds into diapers. Then, I can just pick one up and put it on the baby, no folding or guessing. (And I can also easily grab a few to toss in the diaper bag.)
I have also fallen in love with wool again. I mentioned this on another thread, but I have a problem with my babies being too fat to fasten a prefold on them with a snappi. The correct length isn't wide enough, the wides are too wide, and the long ones just have ridiculous bulk, and I still have trouble making the edges meet. (I've bought a lot of prefolds, can you tell?) If you can't fasten on the prefold, then you can't do a pull-on style cover. BUT, I just discovered how to fold dh's old t-shirts into diapers, using the sleeves as wings to snappi. Beautiful. And so cute. And cheap.
I think I may sew those into fitteds though, because when they #2 and it gets in the wrinkles of the t-shirt. Well, let's just say that's no fun. I decided that that particular t-shirt had been in dh's rag box in the garage. It had already been considered trash. There's just some things I can't do in the first trimester. So, there...consider yourself warned.
Oh, and if you want a wrap style wool cover, you can get them fairly cheap from wallypop.net. I do find that my chunkier babies are not a great fit with the these wraps, but we can make do.