Hi sgogeta4,
There is more about the pros and cons of different types of mattress protectors in post #89 here. Some (such as the St Dormeir that magpie suggested) can help with heat issues and some (like the thin āsemi breathableā membrane type) can make things worse for some people.
There is more about sheets and different fabrics in post #7 here and the posts it links to but if you are looking for the coolest sleeping sheets then my vote would go to linen.
magpieās suggestions are also great.
Phoenix