I am overheating on my mattress in the night

Good Morning
My wife is 10 stone I am 14 stone 5lbs. We have a 3000 Pocket sprung mattress bought last year which is lovely in winter. I, on the other hand am waking up baking against the mattress in the night. So much so I have to remove the covers and sleep nude under a cotton sheet. Whilst this is acceptable, my body cools but where it touches the mattress it is very hot. Sheets are cotton and the duvet is duck down 3 tog for summer. I think the mattress has horse hair and wool in it.
My best sleeps ever, believe it or not come in japan when I sleep on the floor on a futon. The Bamboo seems to keep me at the correct temperature all of the time.
Is there a mattress topper I can use to assist me with keeping my body cool please?
Many Thanks