[ZloyPetrushkO]

ZP's Atmosphere mod is a good starting point (it modifies more than just the cloud textures). Download it, then open his DATA.cld file and start increasing the value called BASE_R_DISP (try 3.0, then 3.5, then higher if you like). The higher that value goes the better the clouds get, but your FPS will really take a hit so find the right balance for your machine.

with your mod(FPSboost) and after editing this parametr(i set 4 or 4.5) there are solid clouds in cloudtype 6+
without your mod it is unflyable