Hi, My baby is 7 months, not rolling over completely in her cot yet. Is there an age that you consider a wool underlay under the sheets safe? Thank-you, Lydia

Red Nose recommends that you use a firm mattress for baby.
If the woollen underlay takes away from the firmness of the mattress, then it would not be recommended for use.
Never put soft bedding under the bottom sheet, such as a sheepskin, as this makes the sleeping surface too soft
https://rednose.org.au/article/what-is-a-safe-mattress

This is especially important as your baby is learning to roll, so that when she does roll to her tummy, the mattress is still firm, & not a soft surface as may be created by a woollen underlay.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over