My son is 11 months old and a friend has recommended using a comforter. In particular a kippins comforter. Is this still a risk for suffocation at his age? What age can I introduce a comforter?

Red Nose has the following recommendations for the use of soft toys/comforters.

Keep soft toys out of the sleeping environment for babies under seven months of age because they may cover the nose and mouth and interfere with breathing.
The risk posed by suffocation by the presence of soft objects in the baby’s sleeping environment outweighs any benefit to the baby from a soft toy.
It is therefore advised not to place soft toys and other soft objects in the cot for babies under seven months of age.

Seven-month-old babies are more likely to explore objects in their sleeping environments than younger babies.
Some babies over seven months of age may appreciate a small object such as a soft toy to provide comfort and connection (transitional object) during times of separation from their parent.
https://rednose.org.au/article/soft-toys-in-the-cot