Insulating under floorboards - I could try myself?

[Kam1984]

I am having my kitchen diner tiled next week. One portion of this will have electric UFH. My tiler will not use any of the branded insultated 6mm backer boards - he said especially over the flooboard sub-floor section he wants to use a full cement board - hardiebacker.
I'm now getting pedantic about losing heat downwards. I have an exposed floorboard area. and I have a week without the kids at home.
I would like to carefully remove some / most floorboards - friction fit PIR boards between the floor joists - I will nail thin wooden battens on the underside so they can sit on them... and then I'd like to put the floorboards back on.
How hard would this be? Its 10sq meters, no obstacles, fully square room.
Will the floorboards go back on?They are T&G - so i have learnt I need to sacrifice 1 T&G to get access, then I crowbar off 1 board at a time, whilst retaining the T&G system? When I put them back on, will they slot into place? Shall I then nail or screw new holes?
Or should i put 4 sheets of plywood and put them down instead? Issue is i dont think i'll be removing the boards right into all of the corners if I don't need to.

I've ran the numbers through chatgpt - I am aware I am not going to save much in electric. It will only be used for comfort / foot warmer - as the area has excellent radiators and most of the area is a new extension. But its more of a DIY attempt. I think the insulation boards will be approx £100. some tools will be £40-50.

 

[foxhole]

Why not use a tiler who does want you want?

 

[Kam1984]

Why not use a tiler who does want you want?

He has a point RE to not soley use insulated backer boards. He said they're not a direct replacement for cement boards over floorboards. I've called warmup and marmox and he is right to some extent. Even if they were strong enough - The insulated boards needs to be glued down. Some parts of the area to be tiled is already tiled on existing backer boards we will reuse - so it could cause height differences.

I'm at a place that I have a week with not much else on and whether I should insulate under the floorboards instead. It'll improve heat retention in my tiles over the living room space.
Using 70mm of PIR will be superior to the 6mm cement coated boards anyway.

I'm just worrying about lifting and replacing my boards.