the (expensive) space blanket in silver rolls is actually yellow fibre, which sheds dust and loose fibres when the cover gets torn.
I only use Knauf mineral wool now, which is treated with Ecose and has a soft feel, the treatment prevents it shedding fibres. It is sometimes own-branded in the sheds, but will alweys have the "Ecose" name on the packaging. It is brownish, not yellow.
You can cut it with a breadnife to fit the timber spacing.
Last year there were lots of energy-saving subsidies on insulation, but there don't appear to be now.
See what price your gas and electricity company, and local council, are offering to supply and fit, they might still have subsidised schemes on offer. Look at BG first even if you are not a customer.