Hi mattressseeker,
You can read more about the pros and cons of zoning in this article and in post #11 here and post #7 here.
There is more in post #14 here about the many reasons for pricing differences between different mattresses or different retailers or manufacturers.
There is more about the pros and cons of different types of mattress protectors in post #89 here. If waterproof or at least highly water resistant is important then one of the protectors that has a waterproof/semi breathable membrane would be the most likely choice or for those who are looking for more natural or organic materials a wool puddle pad with an additional stretch knit cotton protector over it would probably be the best choice.
Phoenix