Insulating the attic is one of the best way to improve insulation with little effort, I have heard. The cost of getting insulation is limited and there are no structural changes that is needed. In theory it is just a matter of spreading out more insulation. I started out in one corner of the attic and moved around all the stuff we have up there as I added 7 cm sheets of insulation. I added as much as possible while still allowing air to circulate above the insulation. It was a lot of work. If I where to do it again, I would empty the attic completely, and then pay a company to come and blast insulation all over the place. A lot more easy, and probably slightly better when it comes to cover everything without any leaking cracks.
Summary in Norwegian: Jeg har etterisolert loftet. Skulle jeg gjøre det på nytt så ville jeg ha bestilt noen til å blåse ut isolasjon, for å krype rundt på et trangt loft var svært anstrengende. Men det ble veldig bra til slutt.