It is really not necessary to buy body gear for standard mountain biking. I think it just gets in the way, its heavy, expensive and hot. The only thing that has ever given me confidence is riding more singletrack, riding with people who are better than me (watching them do difficult sections) and learning more about the techniques used in mountain biking.

Examine the situations when you hit the dirt. Think about what happended, why did it happen and how could you have approached it differently? And if your not sure of something, dismount and walk it. Then you can determine if you want to ride it or move on to the next thing. Good luck.