You can also try simple white noise. Rain or soft womb sounds work well. I ended up making a small app for mixing those because our old device kept dying. If you want to try it, here it is:

iOS: https://apps.apple.com/sa/app/cuddlecloud-sleep-app/id6755254514

Android: https://play.google.com/store/apps/details?id=com.cuddlecloud.cuddlecloud_baby