Recommendations?
Tongue and groove solid oak and it's going to be secret screwed on top of our existing floorboards.
Fibreboard such as this would be the cheap option:
https://www.screwfix.com/p/diall-wood-fibre-underlay-boards-7m-15-pack/7824R?tc=DX3&ds_kid=92700065751868351&ds_rl=1249407&gclid=CjwKCAjw9qiTBhBbEiwAp-GE0WgXTOnIQQ83W4XoTzYXXNLGwx-KXWmGpyz0C4tAGxT2EYbch4adOxoCG0gQAvD_BwE&gclsrc=aw.ds
3mm cork?
Used loads of that stuff for laminate in every bedroom and landing upstairs. It works perfectly. Easy to cut with Stanley knife and straight edge.
I've just done the living room in engineered oak using this stuff.
It has a built in vapour barrier. The floor below is concrete so I wanted to be sure. Only be down a week but it was very easy to cut with scissors and the very useful 1cm grid printed on it.
I bought a couple of rolls of reflective on one side, foam on the other side from our local flooring place. I too had some concrete floor and existing drafts. I tucked it right under skirting in an attempt to reduce drafts even more.