Richard Weir
Hello Clare, To do this efficiently you must insulate the floor of the loft first, then build an independent floor over it upon which you can store your boxes. Please don't attempt to insulate the underside of the roof as the roof will be what is called a "cold roof" which means it is very well ventilated to preserve the roof structure and will never be warm. Post the job on Rated People for the best response. Good luck.
