You want the chocolate to be high quality, which is why we always use Ghiradelli. They have multiple chocolate bars with natural cacao ranging from 60% to 92%, try to use one in the 60-70 range. For the outer coating, the key is to not overheat the chocolate to keep it from separating. If you don't want to use candy wafers, you can also melt chocolate chips (if it's good chocolate) or temper your own chocolate.