Looking good Antoine.
I don't think you need to do anything about the density.
If I look at the background they already look denser, which is logical given the type of POV you're having here.
I think it's pretty accurate.
Sometimes it helps to put some trees in it to create a better sense of scale and thus better sense of density you'll need for your clouds, depending on what you're trying to achieve of course.
Cheers,
Martin