Woodless pencils, like many drawing pencils, come in different grades. I tend to use 4B the most. The only downside to using a woodless pencil is its breakability. Once it rolls off the table, expect to find it in a few pieces on the floor. The fragmented pieces can be sharpened though and are still very usable.
Woodless pencils can be found in most craft and art stores. They run about $2 a piece.
sketch drawn with a woodless pencil