[Closed] Loft insulation - advice needed please!

Moved house last year and got a shock during the winter as the house was freezing yet the heating bill astronomical. The loft is floored and used for storage (which we want to continue), but has no insulation under the floorboards. My mission before the winter arrives is to get insulation down to try and prevent the kids' hands turning blue and further utility bill penury. Pretty much resigned to doing it myself, despite my DIY skills being less than legendary as we're skint. So....

The floorboards look as they've been down a while, might be a bit awkward to get up (with a view to putting back down) but should be do-able. The joists are only 100mm deep, and I think 270mm of insulation is the recommended thickness, so this is clearly not as easy as lifting the boards, laying stuff down and replacing the boards.

I've read a number of different approaches, the most popular of which seem to be either laying cross-battens at 90 degrees to the joists, to allow two layers of insulation to reach the required thickness and putting the flooring back down on the battens, or to fill the existing 100mm depth then use insulating board to make up the rest.

Frankly I think I'd make a disaster of the first method, but wouldn't be shocked to learn its not as hard as I think it might be. The second method sounds appealing, but I can't find out much about using the insulation board with loft flooring. The access to the loft is through a hatch, not tiny but not massive either, so any board in large section might be a struggle to get up there.

We only use the loft for storage, so I want to insulate the floor and have the loft space cold, as its only accumulated crap that's up there. Upstairs in the house is freezing in the winter, even with the heating on so I have to do something.

Like so many things around the house, the more I try and find out before doing something, the more options present themselves and the more confused I get!

Can anyone offer any suggestions? Cheers!