The best insulated plasterboards to use are Celotex...obviously the thicker the better but you will see a very good improvement even using 27.5mm.
https://www.insulationshop.co/15mm_celotex_pl4000_insulated_plasterboard.html
These boards have a vapour control layer...this will stop moisture in the house passing through the board and condensing on the cold solid wall in the cavity. If there is no sign of damp direct bond should be fine, if the wall is damp try to fix the damp issue then use battens or membrane before boarding. Avoid gaps in the boards...seal around the outside with foam.
If you opt for cheap sh*tty thermal boards like polystyrene backed you will need a vapour control layer behind the boards...e.g battens, polythene, thermal boards.
Thanks for that mate. When you say that improvement will be made with 27.5mm boards the link you sent has 15mm or is that a 27.5mm coz of the 12.5mm plaster board attached to it so is that classified as a 27.mm board.
I was looking at these what's you thoughts on these:
https://www.wickes.co.uk/Knauf-XPS-...dB8rdOgDsVwUxJFxAjBoCv6cQAvD_BwE&gclsrc=aw.ds