What mattress protector is recommended for the Artisan Naturals?

Hello,
First, thank you so much for the effort of putting together this incredible site, full of educational information. Like most of your visitors, I imagine, I stumbled upon the site with very little knowledge about mattresses and how to shop for one, after spending a good few hours I felt much more confident and knowledgeable to go into stores and engage with their sales people. Eventually I chose to buy your Artisan Naturals (king size, medium tension) based on my requirements and budget. I received the mattress a few days ago and so far both myself and my wife are delighted with it.
One key message that I took away from your website was the importance of placing a mattress protector on top of the mattress - but I am not sure what kind to purchase. I think a memory foam one would actually have a harder feel to it than the upper layer of the mattress so I would like to get your advice about types / characteristics that would be important to look for.
Many thanks in advance