loft flooring: two layers insulation

I have a large loft of which I plan to floor a few square metres using the normal DIY store boards.
I have to layers of insulation up there. One layer between the joists, the other on top, lying across.
What's the best way to handle this? Just pull up one layer because I'm doing a small area? Or are there other approaches/ideas.

What is the thickness of your ceiling joists? Is your house old or new?

With a modern house You can use loft stilts/legs, available from most large DIY outlets. Info is on the web. They rely on collective strength, rather than individual rigidity, so they will all need to be screwed firmly to the joists and floorboards for the combined strength to work. Old houses might have irregular thickness joists and the top of the stilts are then very difficult to align on a common level to ensure they all fix to the T&G loft boards.

Most modern houses are built to minimum legal standards, to make them affordable. Ceiling joists are not now designed to account for additional weight in the loft. 100mm joists are now very common and they are incapable of sustaining any heavy point loads.

My opinion: if your existing joists are at an uneven height for T&G boards, but closely spaced (400mm centres), well supported across a small span (>3m) and at least 200mm thick, I would temporarily remove the upper lay of wool, fit 145mm X 45mm cross joists (800mm centres to reduce weight) with packing where required. Then re-lay the upper 150mm layer and board over the top. The 145mm joists are heavy which is why the strength of the existing joists must be considered.

Additional joists spread the load a lot better than those crappy stools.