Maybe you should take a look at the plugin FluidNinja, because that have some nice and lightweight effects, that might be good for your clouds. (and the creator might be able to give you settings, to make the clouds not flow so fast ^.^ that was one thing i couldn´t figure out in my short test)
Plugin at the marketplace:
Fast sky testvideo from one of the demo levels i have slightly edited the lightsource 
:
A tut from their discord about how to paint volumetrics:
