Still working on getting the en-suite finished off (my dad's doing it
for me) and he's suggested hardboard sheets to "flatten" the floor a
bit, rather than it going direct onto floorboards.

I have a few reservations though...

The hardboard seems to do a good job of highlighting hollows in the
floor, so while it might be a flatter surface overall, it also bounces
a bit where the underlying floor is uneven.

The back-to-wall units go all the way to the floor, they're not the
sort on legs with clip-on fascias, so he's talking about sitting them
on top of the vinyl - which happens to be the plushest / deepest we
could find (and the hardboard below that) which might make the vinyl
"lift" slightly around load-bearing edges for the units etc.

If the vinyl needs replacing, this then causes problems with
essentially needing to gut the room to get the new stuff in - unless
i'm missing something obvious :-}

The only way around it that I can see would be to run a blade around
the fixtures and fit the new vinyl up to the edges, but that'd look a
bit crap, even with silicone to seal the edges.

Any ideas on best practice in these circumstances would be welcome :-}