Hi NCSteve07.
Welcome to our Mattress Forum. 
Congratulations on picking a stellar mattress. We look forward to hearing about your sleep experience once you’ve been able to test it through the break-in period.
Cotton is a natural fiber and as such is also highly breathable. Cotton is not going to be a culprit in sleeping hot. I also found this thread which seems relevant to your question in which someone mentioned their experience with the Cozypure “Pebble Pique Organic Cotton Stretch Knit Mattress Protector.”
I took a look at the knit cover and can see it is polyester. While it certainly may be breathable, if you’re sensitive to synthetic materials I’d steer clear of polyester which can contribute to sleeping hot.
I hope this helps!
NikkiTMU