Tips for underfloor insulation.
Easiest method is to pay someone else to do it. It will cost more, and in my experience wont be as good a job.
If your doing it yourself, lift all the floor boards. I tried one room lifting only every 5th board. pita.
Personally I would fit, with batons, ridged stuff. ie celotex or similar. Netting + cotton wool style not going to be as good long term. Get it as deep as you can fit with regard to joist depth, you only want to do it once, so may as well go for it. Its a bit more expensive, but will reap rewards in the long term.
Once the insulation is in, get a bucket load of decorators calk (official method) or bathroom sealant (my method) and seal seal seal every gap between insulation and insulation. Seal seal seal every gap between insulation and joist. You get the idea.
Then, ideally you would board it with ply/similar, before relaying original flooring. This adds to the air tightness. Boarding does create problems as the floor level will be railed a bit though. If push comes to shove lay breathable membrane over it before replacing flooring. I actually just used brown paper, to kill drafts, but not sure it was a great plan looking back.
Takes a good weekend to do 1 small Victorian room if you have some help. Some help would be a good bit of advice actually, many hands and all that.