I've been using these for years. They are like the ones you can purchase at the big box stores but these, you won't trip over. They open up and divert the heated air when the furnace blower comes on and close when it goes off.
The plastic sheeting comes from those plastic report folders and they are fastened to flexible magnetic strips with clear tape.
https://www.dropbox.com/s/lbnn6y3287lrdnb/vid_20211208_124852473.mp4?dl=0