I wonder whether you could just build a self supporting cavity wall on top of the new floor? As I see it there are two potential issues: damp coming through the walls, and excessive humidity causing condensation damp issues.
For damp coming though the walls, as long as there is an air gap, it can't affect the inner wall. As you will be aware, cavity walls of brick or block were common construction in the UK during the 1970s and 1980s. But timber frame is the norm now. Your sump arrangement will remove any moisture at the base, so the wall won't be sitting in a puddle.
The main issue you might have is condensation issues due to humidity. A damp unventilated cavity is just what 'dry rot' likes to live in. The humidity could attack the inner wall if of non-durable materials, or cause damp at 'cold spot' where the insulation is thinner for any reason, or inside the insulation itself. Increasing ventilation may help - airbricks or other vents above ground level perhaps.
I found this site (ignore the materials used and just think about the concepts)
insulating basements which might be of some help. It suggests that adding a vapour barrier in the basement walls can cause more harm than good, although does say to minimise water ingress through exterior drainage management. It also suggests insulating the floor, which you may want to consider if you are re-laying it. The more I look at the subject the murkier it gets!
This site gives a bit more information as to whether a vapour barrier may be needed depending on the climate and temperature differentials expected. I also came across foil scrim kraft vapour barrier. If you decide a vapour barrier is wise, then this seems to be plastic free: Aluminium on a paper backing reinforced with glass fibre scrim. A latex rubber based material might be another more
Permie vapour barrier.