I'm doing cloth diapers for three years now. When I was pregnant with DD, friends gave me a pack of 12. BumGenius One size pocket diapers. I thought the pocket diapers were overkill at first, but I soon learned to love them.
A newborn usually can't go very far on his/her own, so diaper changing works fine, even if it requires several layers. However, I found prefolds work better with a polyurethan cover than a woolen one, because the runny poop tends to leak out of the diapers. Fitted diapers work fine with woolen covers. DD had very sensitive skin and usually did better with a woolen cover, because it allowed her skin to breath. DS was a very heavy wetter and needed polyurethan covers, because he tended to pee straight through the woolen ones. On his best days, he went through 16 diapers a day. DD was mostly around 10 diapers a day as newborn.
As my children got older, I found prefolds increasingly inconvenient, because they didn't like like still for a diaper change. Changing diapers on a moving target is soo much easier with pocket or one- in-alls. Personally, I prefer pocket diapers to all-in-ones because they move the moisture better away from the child and I can double and triple stuff them to accomodate DS peeing habits.
The one problem with one size diapers is that they usually don't fit newborns for the first month or two. Some brands have a bit wider ranges: Happy Heinies and Butter Bears are pretty good in catching both very small and very big babies. But even with these brands, having prefolds with covers for a newborn, or fitted newborn diapers is often necessary, because the one-size- diapers don't quite fit yet, and a newborn typically needs more diapers than an older baby, so you would overbuy on expensive pocket diapers by putting your newborn in them exclusively. Personally, I find you can never have too many prefolds at hands, they have many uses. I tend to stuff DS's pocket diapers with prefolds, because they are more adsorbent than the inserts they usually come with. I never used the newborn prefolds, the normal smaller ones just do fine, even on small babies (DD was 5.15 at birth).
The amount of diapers I'd recommend: At least enough, so you don't have to wash every day. So as a minimum I'd start out with thirty prefolds plus three covers. For an older baby, I'd recomment about 20 diapers of whatever style you prefer. That amount allows for at least one wash free day and line drying under less than optimal conditions.
I got most of my diapers at Jillian's Drawers.
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