I understand about laying on plastic. Nearly all mattress protectors are lined in plastic and they do cause me to be hot. However, when I bought my last mattress the store showed me a knit cover that does not have a plastic backing. It has elastic all the way around and stays wonderfully on the mattress. No need to keep adjusting it as I've had to do with regular protectors. This was a store such as American Mattress. I don't know if it was that one and I can't think of other store names.
My daughter and her husband just bought a memory foam mattress. The mattress store also sold them the same sort of protector. The knit fabric has a rubberized feeling backing that gives with the knit. All of us have found these to be comfortable and without the heat that a plastic backed protector causes. And it's kept my mattress as clean as new in appearance.
This mattress protector, I bought, was somewhere around $60 for a double bed size. It's expensive but very much worth it.
BTW Microfiber is a form of polyester, I think, and is hot in its self, too.
I just saw you live in Troutdale. I'll find the name of the store(s) we bought this from.