The Govt here has a scheme to get help get older homes insulated* - they pay 1/3rd of the cost. My wee flat qualified as "older" as it was built before 2000.
Along with underfloor insulation I've had a plastic sheeting placed over the ground in the basement to prevent dampness inside. Before that could be done the basement had to be emptied-
Then the insulation team put in the sheeting and stapled it into the ground, while also pushing the insulation up in between the floor joists.
This insulation is fireproof, and can easily be moved for any work on the wiring or plumbing.
Zebby stayed under his quilt while it all happened, and the first time he stepped outside the front door afterwards he refused to go any further - there were strange things under the clotheline! Eventually Zeb realised the old doors made a handy spot for playing "King of the Castle" and sunbathing.
Once all the junk from the basement had gone (whisked away up the demon steps by some rubbish removers) Zebby's garden was peaceful again with just the daisies for him to contemplate.
* there are similar insulation schemes in some Australian States