I have spent the last three weeks trying to make realistic volumetric 3D clouds in Unity.
I found some free clouds that were not fluffy.
I made some volumetric clouds in Unity but could not make them fluffy.
I make some fluffy clouds in Blender with cloud generator (www.youtube.com/watch?v=EpGdRJFPVEI) that would not go into Unity without losing their fluffyness.
Finally I found this excellent free cloud toy (assetstore.unity.com/packages/tools/particles-effects/cloudstoy-35559). As I didn't have the source code, I made a script that detected when the clouds were spawned and then added rain to them.
Next step: realistic looking dry stone walls.