Having a firm flat mattress for infants to sleep on is an essential safety measure. Australia has led the way with mattress safety, having developed an Australian Standard for mattress firmness in 2013. This initiative is now being introduced internationally now with the United States of America adopting the requirements in their safety standards.
Do not use a mattress that is not firm or flat.
Do not use an inclined sleeping surface for an unsupervised sleep environment.
Never add an additional mattress to a portacot. The mattress supplied with a portable cot is suitable and safe.