Andy, once practicing at shallow water, you may want to try to improve the low-wind gybe too. When tacking, the board can come to a complete halt or even sail backwards. The board gives you the least support when you need it the most. Though you loose some height gybing, the board is moving all the time and thus more stable through the manoeuvre.
Try this: Once the board is starting to turn downwind, sheet the sail in. It might feel counterintuitive at first, but it works well. At some point the wind will start to flow clew-to-mast and will pull you immediately to the new direction. You sail clew first and can wait with flipping the rig until you feel stable.