Wool Underlay in Cot?

When DD was 2 weeks old she went into the childrens hospital to have several tests done. During her stay they used a wool underlay in her cot. It looked so comfy that when I got home I brought one only to find out that SIDS do not recommend these. So I took it off. Something about dust mites I think.

I am thinking of putting it back in as she mattress is SOOOO hard and she has a very flat head (mainly due to being in a hip spica plaster and brace for her hip) and I thought this may help plus it may be more cooling in summer. Plus I figured she cannot roll in bed cause of her brace so its not like she can smother her self with it

Does anyone use one of these wool underlays? Is it safe if I air it out weekly? At what age does the risk of SIDS decrease?

Thanks,
Cath

I think once they are starting to rolla round it decreases - so from 8m onwards? But I think it really doesn't start to drop around 12m.
We just have a woollen blanket under Jenna's sheets - its what I've always had under sheets, so I just automatically did it with hers.
Maybe someone else will jump on and give some more advice.