Potty training, mattress protector (Philip Lane, N15)

Hi there :) we are about to attempt to start potty training our three year old again and I would really appreciate some bits to help out. We have potties, but a travel potty would be really useful. I had a Potette but he refused to use it so got rid of it. Any waterproof mattress protectors would be amazing. I am going to buy one but I need extras. Thanks in advance!