cold store

[Dasha]

I know that warm air rises but my first floor bathroom which is situated above a store room on the ground floor is very cold in the winter time. The wooden floor in the bathroom is the store room ceiling. Is there an easy way to insulate it? Does cold air rise or is it just draughty, even though I've tried to seal up all the gaps.
Thanks* :?

[welsh brickie]

there are many materials to use fiberglass,celotex boards etc.
I would suggest using fiberglass wool its cheaper, just pack it in the whole ceiling and board over.