The blue node works alright, my Cirrocumulus started off with voronoi diff scalar, but the noise was just too hard despite smooth stepping and such. Like Dune said, a PF would probably be a better choice.
Have you also considered using the Redirect Shader as a warper, with 1-3 PFs on each axis. You can create some really interesting effects with it, especially with X-Z with different PFs as the redirect will alter between the two directions and create cool effects.
Speaking of the Cirrocumulus you might check it out. Combing these shapes you already have, or a new voronoi setup with a PF with the technique I used creates more realistic clouds that you'd see IRL with these patterns, where boundaries often wisp out or transition away.