This is a simple bumper that slides onto a corner of the headrest of an Ikea MALM bed.  It will stay on well enough with friction, but I used a strip of double-sided adhesive just to keep my kids from yanking the bumper and throwing it like a ball.

This must be printed with TPU (flex filament) in order to work as a soft cushion.  I used SainSmart TPU with a Shore hardness of 95A, but anything comparable should be fine.  I printed using the 0.20 SPEED setting in PrusaSlicer and with only a 5% infill.  You can see from the second photo that it will compress under pressure, but it bounces back immediately afterward.

The .gcode file gives an estimate of 6 hours and 24 minutes, but I always reduce my printing speed to 50% for TPU to avoid problems, so it took closer to 12 hours on my MK3S.  Adjust as appropriate for your own printer.