I had an exercise mat in the house. I rolled it up, put duct tape around it and have been using it as a heavy bag. I put it on top of a stool in the corner of a room.
You don’t get to do the footwork as with a hanging bag but for just throwing punches it’s great. It’s also softer than a heavy bag so I don’t even need to wrap my hands.
Easily the best idea I’ve come up with. I did a lot of boxing training back in the day but my hands are better than ever.