Ultra warm but waterproof bedsheets?

Share your ideas about the practical side of caring.
Is it just me, or do those plastic bed sheets make you/your caree feel so cold?

I've got a lovely new memory foam matress from John Lewis, so I don't want to wreck it with nighttime leaks and my smelly sweat (yeah, my sweat smells of ammonia these days).

So I made sure to use a plastic undersheet. But now the weather has turned, I'm finding the plastic undersheet makes my back and bum so cold that I get spasms. Spasms so bad that I huff and puff, and my eyes roll back in my head. :roll:

I got a sheepskin rug to sleep on to sort that out the cold problem. Working well so far. But now I'm worried about having to wash it a lot if I have night sweats or leaks.

Where the heck is bedding that is ultra warm, easily washable, yet will protect your matress? :-???
Would a waterproof mattress cover and regular sheets help?
I've sent you a pm as I'm not sure what the rules about recommending specific products are on here. I found a site selling things for children that had some brilliant (but pricey)protective sheets in adult bed sizes.