Insulate under floating floor below grade?

Hi-

I'm thinking about installing a floating laminate floor in part of our basement, over existing vinyl tile/concrete. The basement is 50+ years old and dry, block walls are properly insulated and finished, but of course the floor is cold because they did not insulate under slabs back then. What's the best way to add a layer of insulation under the laminate? Options might be Reflectix (foil-faced bubble wrap) or rigid foam perhaps, but ideally not more than 1/2" because we're working with

-kiwanda