I am converting my basement into living accommodation. There is a screed floor with DPM which appears to be dry. I am unsure how to proceed with new floor, bearing in mind I don't want to lose much of the 2390mm height. To maximise insulation I am considering laying 50mm or 75mm of kingspan insulation directly onto existing floor and then lay 18mm plywood on top, secured by drilling through insulation. Alternatively I could batten out with 3x2 layed on its edge and inlayed with 75mm of kingspan and lay plywood sheets on to battens but concerned about cold bridging. A final idea is to lay new screed with underfloor heating. What's the minimum depth I could get away with?