Deville wrote:
Any reason why these can't be laid straight onto the existing
chipboard floor? I'd like to avoid an extra layer of plywood if
possible.


Been there, seen it, done it (albiet with ceramic floor tiles).

Lasted 2 days before I gave up, ripped them up (after spending an age
cutting them around the furniture) and replacing with laminate.

Short story - the floor was not stable enough, and the grout / bonding
agent not flexible enough. I've since seen more flexible adhesives but
unless there's been an order-of-magnitude improvement between these and
what I used some 3-4 years ago then I'd be nervous about tiling onto the
chipboard.