Your own body? Carrying it very close to you, under the anorak, only getting it out for a photo and then back into its warm(ed by you) place? And - this is what I read on this very forum in other discussions, too - carry the replacement batteries in your trouser pockets, close to you, to also keep those warm so they don't drain by the cold only. I also read about mittens to wear (under a pair of thick, warming ones) that have nothing where your fingertips are so you can feel the controls. But you would also only let your hands out for as long as you would let the camera out.
OK, this is all things I have read on here before, others might be able to give you much better advice. Or you might want to browse the forums for the information ... there has been a similar question going on only a couple of days ago ... :scratch: ... use the "Search" function for it, maybe?