Good work, Have the same problem with a 11 year old b and q kitchen and luckily have a wrapping company at work so will get some offcuts out the skip and try wrapping the J handle recess which would be the tricky part, Thanks for the inspiration.
First i am not a decorator but a dark matt colour in a high traffic area will mark easily and that's from my own experience, someone will advise about the prep im sure.
I'm not a sparks but would check that the conductor is not damaged(with the power off) and tape up if ok but am sure someone more experienced than me will advise if incorrect.
I used these but they all seem to be 175mm but you have to add the ceiling to joist height.
https://www.amazon.co.uk/Loft-Insulation-Boarding-loftlegs-Legs/dp/B00AZLJ7GW