No advice on the mattress. When I was in the full throes of hot flashes, I used a small fan directed at me, very light bedclothes, and just a t-shirt/underwear for wearing to bed. We both like the house cool, so that wasn't an issue. We'd keep the air conditioning on all night when needed. I tried a lot of homeopathic stuff that was supposed to help hot flashes but none of it worked for me. :-(
I'd try the "cool" pillow idea, that sounds promising. Good luck! I hope your flashes don't last as long as mine.