You don't need to lower the boom nor buy a "waterstarter." Just place the foot of the sail on top of the (back) board before starting and you should have no problems. I use that method f. ex. with my 9.0 and 155 Go.
Earlier I had similar problems with the clew sinking down and bought the "waterstarter." It was some help but you don't really "need" it in order to perform ok.