You could use a cloud texture and lerp it through two different versions of the same texture so it gets a more random look. If you set the UVCoord node to i.e. world location or just a random number it would all look more random.
Here is the basic LERP setup using a noise / breakup black and white texture to blend between the texture and a color, but you can do as Luos says and use two different textures as well.