Given that cot bumpers are unsafe, what can I do to stop my one year old baby accidentally bumping her head on her cot during the night?

Red Nose has the following information about cot bumpers.

Older babies in a cot can be at an increased risk of a sleeping accident by using pillows and bumpers as a step to climb up and fall out of the cot.
It is safer to wait until the child starts to sleep in a bed before introducing a pillow or other soft bedding.
https://rednose.org.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows

There is also no evidence to suggest baby will cause any serious injury by accidentally bumping their head on cot sides.