Any tips for lost comforters in "big bed"?

[MyNameIsInigoMontoya]

DS is just moving from cot to big bed, and at the same time from grobag to duvet and pillow. But both nights he's been in the new bed so far I've woken to hear him crying as he couldn't find his comforter (little blanket with an animal head). The first time it had partly slipped down the side of the bed, but last night it was still in bed and not far from him but he just couldn't find it.

I suppose a small nightlight might help but wondered whether you had any other suggestions to stop it getting lost? He does want it when he wakes so I don't want to keep having to find it for him! Thanks.

Could you get one of those elastic clips that goes under the mattress to hold the duvet in place? The elastic stetches under the matress and two plastic clips hold the mattress a bit more firmly in place (but not so you can't move about in bed)
Might not help but could stop the duvet moving as much and hiding his comforter.