Insulating an overhang

I've just moved into a 1920s house which has some quite eccentric features. One of these is the two front bedrooms overhang beyond the downstairs.

One room was insulated by the previous owners - don't (want to) know what with but it seems to work.
The other room has a bigger overhang - it sticks out over wood/glass the sort of porch below. Now I've taken up the carpets it's pretty drafty and this is blowing right through the house as the joists lie that way. It also seems to be wafting some not to pleasant aromas around - but that's another story.

Anyway, I want to pull up as few as possible floorboards and get some insulation down above the overhanging section. I thought about just stuffing loft roll in their, but would like to know whether there is a better way to go.

Thanks,
Chris

Yes, take up all the floorboards and do it properly.

Celotex and rockwool, 100mm each.

Thanks for the quick reply.

Is that Celotex down first then rock wool on top? Anything else I need to know or is it just a matter of cutting it and putting it down.

I'd put the celotex directly under the floor as it's the better thermal performer. The rockwool at the bottom serves for better sound insulation