-
Your friendly local planning permission place might have all the standards online (the NI planning board does, you have to declare insulation for inspection) and Youtube is very good too.
I second buying wool insulation, be aware wool can be eaten by moths if not treated. But there is special wool insulation, everything at BnQ here in Belfast is selling out too. Only 10 cm rolls left (ffs)
You get the risers that sit on top of your existing joists and board on top of those. You just fit the insulation around the services, making little cuts here and there when needed.