Hi! I am new to cloth diapering and have a few questions. A friend of mine gave me some Thirsties Duo Wraps (covers) and 2 inserts (they are doubled, polyester on one side and cotton/hemp on the other side) and 2 prefolds. I've been reading that a fitted diaper goes under the covers, but why can't I just put the inserts or the prefolds under it? Do I have to spend the money on the fitted diapers or is there a cheaper option? I am so new to this and I just don't want to spend unnecessary money! Thanks in advance!