I’ve been trying a rolled up towel but it gets soaked and falls into the tub if I lean forward.
Twist the towel like you’re about to snap somebody with it.
Then curl it around in the shape of a ring at the back of your head and lean back into the hole in the center.
Do it tight enough and it should stay as long as you don’t lean forward. You can always hold it closed when you do though
Pool noodle
You can also use a pool noodle to line the bottom part of your door if there’s a gap so you can keep the bathroom nice and steamy.
There are ones of various shapes that suction cup to the wall or tub.
This is the one I bought not too long ago. I have a similar bath setup as you and was looking to solve the same issue you’re describing. So far no complaints. https://a.co/d/grkdDxF
NO.
Seriously…try one of those silly inflatable pillows for flying. But be ready for some headbanging!