I sing soft lullabies as part of bedtime routine for my daughter. Sometimes if shes too unsettled i’ll look up lullabies on youtube and let it play until shes settled. It will play very soft versions instrumentally.

When my eldest kids were very young I played Celtic lullabies. With my youngest now I don’t play music, just sing 1 or 2 songs as part of the bedtime routine and then it’s light off and time to sleep.

I had a disc called Sanctuary that contained lots of soft music with birds tweeting – it was very relaxing. You could probably Google “ambient music” and find something you like.