I think to match the reference more closely you will need to both have a subtle texture animation AND have a dynamic density. Fortunately there is an aspect of the cloud behavior that is a bit like a density moving through a texture that is slowly animating downwards.
Make the density and velocity grids dynamic on your scene and make the opacity input= density instead of constant. You can either paint the initial state of the clouds or emit into them and set initial state from current. Given that you are painting the cloud density you may wish the opacity gradient ramp to shift to the left a bit. In addition to the initial state you may also wish to have several emitters for the clouds, perhaps with density dissipation.
Initially I would try and just do a simple fluid animation… a few blobs of density moving slowly and shearing a bit with most of the detail and motion in the texture. (you might not want any density buoyancy, perhaps just push the fluid with a weak force or have some speed on the emitter)
One could try a more complex simulation, for example one could have a large flat volume cube emitter at the bottom of the fluid with high turbulence on the emission so that it has a chunky emission, perhaps also emitting heat into the simulation. A problem I’ve found, however, is that simple rising heat makes the fluid become streaked upwards like flames. I think one wants more little localized upward puffs within the fluid. There is a lot going on so I’m not sure what is the most critical effect for the visual look of cloud formation. In addition to an emitter along the bottom of the fluid one might also want an emitter towards the top that sucks density out (use the replace method on the emitter with density = 0 and emission rate relative low with dropoff). One might also have a replace of temperature in a similar fashion on the same emiiter. This could simulate the effects of change in pressure and temperature with altitude.
If you go for a more complex simulation you may want more resolution on the fluid grid and less texturing. One can increase the texture frequency and lower the depth max, essentially replacing the low frequency iterations of the noise with the grid based fluid density. At a certain level of complexity one could do away with the texture altogether, although it will be slow to simulate and you might run out of memory.
The rendering should probably also use shadowing( currently the shadows on that fluid are faked with a y gradient incandescence ramp that is also textured ), but you probable don’t need to turn on real lights. Ambient diffusion would also help. Mixing the clouds with a sky fog fluid can help to make them blend into the sky, instead of being in front of a sky texture, although it depends on your camera viewpoint.