What mattress protector is suitable for an Artisan Naturals?

There are some extravagant (and some costly) mattress protectors out there such as wool toppers but seeing the sumptuous layers on the Artisans Naturals do I need nothing more than an extra sheet?Then again, there are waterproof sheets but surely these act as a membrane and counteract the breathability of the materials used in the mattress?Going full circle, perhaps the wool topper is the way to go to give breathability, some absorbency, washability and ultimately protection.