Where can I purchase a waterproof mattress or a mattress pad that really works?

You can get waterproof mattress covers at most retailers that sell bedding, I purchased ours at Walmart. Major drug stores will carry both washable and disposable pads to place over the sheets, the washable ones are also helpful as re-positioning aids. As for a better pull up than Depends, I used to prefer Tena but am finding that they are no longer up to the task. Some have luck adding a poise pad inside the pull ups, there are also booster pads specially designed for this but I haven't found a retail location that carries them, only online. If you shop online there are several heavy duty brands of diapers, Tranquility is one.