I have a 9 monther in a 20 gallon long and it is PLENTY big enough for her.
Most people 'round here say that a 10 G is big enough for hatchlings, and that the rule is that the length+width of the tank should be >= the length of the snake.

Also, there are plenty of people around here that LOVE the coconut stuff for bedding, but I have also heard it can be messy