I would like to have a warmer TC floor... any ideas?

for a non-permanent solution that can be pulled up anytime and used again: thin foam underlayment and then use carpet squares (18") available at Home depot. The squares have a plastic sheet on the bottom, just peel off and stick them to the underlayment that you can precut to the dimensions of your TC floor. That way you can just remove the whole thing whenever you are ready as it isn't attached to the floor.