Floor of converted garage is cold, what covering can I add?

I have a garage inside the thermal envelope of the house that I converted to a room. Garage door was replaced with a well insulated 2x6 wall, and walls were done to a high standard.

Unfortunately the floor is the weak point, while I have 2 inches of XPS under the poured slab, on top of the slap I have plastic dricore followed with vinyl flooring.

It's very cold and I'm kicking myself for not putting foam underneath. Too late for that, but I was thinking of putting carpet with a heavy foam underlayer.

The room is used as a entrance, light duty workshop space as well as storage, so I'm thinking of a durable low pile commercial wall to wall carpet, but I'd like to put as thick a layer underneath as I can.

What should I go with?