Loft ceiling insulation

[Zampa]

Right then...

Im looking at somehow insulating and boarding the ceiling in the loft/attic..

I have looked at a couple of options but im not sure if im going down the right route

Option one..

lag between the rafters using 'space blanket' then over boarding with plasterboard, problems I can see with this are..the centres are 400, the space blanket is 370..ok only 15mm each side but will this impact on the actual insulation qualities?...
The other probem is the re boarding, the boards will have to be cut down into 600 'strips' in order to get them through the loft hatch...all this obviously adds up to a lot of graft...

...all this should top up to about 170 quid max

Option two..

Board straight over the rafters with celotex 2 inch insulation board..is similar to kingspan by the looks of it and probably cheaper..I would grip fil it to the face of the rafters..a simpler more straight forward job, even though, again I will have to cut it to size..however this comes in at 300 quid..

So..

Question...which of the two options will be the most effective?

Question...will the fact that the space blanket is a bit short make a difference?

Question...Is there another way?..traditional lagging between the rafters is out of the question due to the 'itch factor' and the loft is full of 'stuff'

Thoughts?

Thanks..