Do you fall because of tremors or because your legs are rigid? If so, DBS might help. If you are falling because of postural instability and balance problems, DBS usually does not help these symptoms.
The ideal DBS patient is one with a lot of tremors, dyskinesias, and fluctuations. Essentially what DBS does is take your best "on-time" and stretches it out.
Your physician can give you a DBS dvd put out by medtronic which can answer at least some of your questions.