Went to my Wickes the other day for a pack of 5" T&G floorboards to do
some patchwork repairs to the floor following some plumbing escapades:
however it emerges that the new ones are 17-18 mm thick compared to
20-21 mm for the old ones. I'm presuming both are nominally 0.75"?

Should I be able to get thicker boards, or are these new ones now the
'norm'? It's a right PITA: the thickness difference is definitely
enough to be noticeable on the floor, and also the T's and G's don't
match up either.

If I do have to use these, I'm trying to think what I could use as
packing? It's too small a gap for any form of plywood or hardboard.

David