Looking at this reference, several ideas I have:
Create a base planetary cloud fractal (Power fractal shader), with some warping etc (although I don't really like TG's lead-in warp inside the fractal, seems to create noticeable artifacts). Then duplicate the layer, say 3 times, and offset the clouds slightly. Then use fractal warp shader, with large scales, and with slightly different input params.
Fractal warp is the key to get wispy stuff in TG in my opinion. You could also look at doing an altitude offset using a fractal mask, and have the clouds 'fade out' down into a hazy lower atmosphere, that the reference you posted seems to suggest.
Otherwise I would look at creating an image map based on Earth clouds, or look at this that WAS posted the other day:
https://planetside.co.uk/forums/index.php/topic,29403.0.html