Originally Posted by chephy

Actually the obvious solution is "practice". Try straddling the bike, putting one foot on the pedal, pushing off with the other foot and just coasting for as long as you can (make sure that you're leaning slightly towards the free foot so you can catch yourself if the bike starts falling). It might even be helpful to remove the seatpost from the bike to practice this, or you might find yourself still putting your butt on the saddle just because it's an instinctive motion at this point.

Do practice and master it. You say you have a history of knee problems, and hence afraid of falling. I say you if have a history of knee problems, you should be afraid of wrecking your knees by having your saddle too low. ILTB can call me an overreacting drama queen who should get a grip, if he wants, but it really isn't good for your knees to have the saddle too low, and wrecking your knees is a tragic thing.