I'm planning to install an engineered hardwood floor on a concrete slab that is very very cold. The climate is northern New Mexico. The slab perimeter is not insulated, and doing so is cost-prohibitive at this time as it requires removing more concrete that abuts it, some of which is structural. The slab's thermal mass is not contributing much if anything to moderating internal temperature conditions due to the house's siting being unable to take advantage of much direct solar irradiance. All it's doing is making the house cold.
So I'm thinking of applying polyiso foam insulation board over the top of the slab but below the new floor, basically cutting off the thermal mass of the slab from the interior climate. If I were to do this, where should the moisture barrier go? Between the bare slab and the insulation board? Between the insulation board and the wood floor, perhaps with a moisture-barrier-type underlayment? Would I even need a moisture barrier at all with this setup?