You may or may not need a special solution for overnight diapers. When I started using cloth diapers, I was very nervous about using cloth diapers overnight. The last thing I wanted to do was sacrifice precious sleep. It turned out my son was just fine in a prefold, a doubler and a regular PUL diaper cover.
Some babies, however, are heavier wetters (or longer sleepers) than others, and you may need more serious tactics, such as specialized night time diapers, to keep your baby dry overnight.
A diaper doubler may provide all of the extra absorbency your baby needs to get through the night. There are plenty of companies that sell diaper doublers. You'll find a list of them, as well as more information about diaper doublers here: Diaper Doublers
You can use a prefold diaper as a doubler (so you'll end up using two prefolds to diaper your baby). Fold the first prefold using your preferred method. Fold a second prefold in thirds and lay it along the middle of the first prefold, then secure the diaper on your baby with a diaper cover (use pins and/or a snappi if you like).
If your baby is older and you have some infant sized prefolds left, you can use these as doublers. They will be a little less bulky than the larger sized prefolds.
Using wool diaper covers can give you a boost in absorbency. Wool is extremely absorbent, in fact, it can absorb about 30% of its own weight. several companies manufacture wool diaper covers. You can find a list of popular companies that sell wool covers as well as more information about wool diaper covers here: Wool Diaper Covers
Some fabric is more absorbent than others, so whatever night time diaper solution you choose, look for products with extra absorbent fabrics like bamboo, hemp and microfiber to keep your baby dry all night.
Some companies make night diapers specifically for overnight use. These night diapers tend to be a little pricier. Using doublers or prefolds is the less expensive solution to overnight diapering. However, you'll only need a couple of specialized night diapers, and if specialized diapers are the best solution to the problem of night time wetness, and if they are going to buy you a few hours of extra sleep, then they can be well worth the price.
Overnight diapers cost approximately $30-$35 per diaper