Hi, I've seen silk slips for cot/bassinet mattresses bring advertised as a way to avoid a bald spot on babies head - assuming they fit snugly on the mattress, would these be SIDS safe? Is there any research on different mattress sheet materials impacting SIDS risks? For example see silkytots.com

Red Nose does not suggest any specific type of material for cot/bassinet sheets, but recommends that any bedding is a tight fit, so that it does not become loose creating a risk of baby’s head & face being covered,
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep

Balding or flat spots on baby’s head are not uncommon, but can be reduced by practicing tummy time from birth when baby is awake.
https://rednose.org.au/article/tummy-time-is-good-for-baby-because