Hi, My mpartner and I follow all the guidelines, but I'm still a bit confused and paranoid as SUDI refers to unexplained. Does that mean even if there's no object in the cot for them to suffocate on, they can literally just die in their sleep? E.g. just stop breathing? It's really affecting my sleep as I cant help but to check on her all throughout the night to make sure she's still breathing. When her breathing is really shallow I also get anxious. She's 3 months. Thank you!

Safe sleeping recommendations refers to more than having a soft toy or comforter (or other soft objects) in the cot.
https://rednose.org.au/article/what-do-the-safe-sleep-recommendations-mean

You are correct, SUDI is an unexplained event, however, research over the last 30 or so years has shown us ways to reduce the risk of this unexplained event.
As a result of the 6 Safe Sleeping recommendations there has been ab 85% reduction in the SUDI rate.
Also, over 90% of the deaths that continue to occur today, risks have been identified in the baby’s sleep environment.
The risk to a baby, where Safe Sleeping recommendations are being followed is very low.
https://rednose.org.au/article/what-are-the-risk-factors-for-sudden-unexpected-death-in-infancy-sudi
https://rednose.org.au/article/can-sudi-be-prevented

I hope this provides some reassurance for you in relation to your baby.