I really like this; your shading looks great.

For the background, what about a coastal plain? You could have a horizon line, maybe the suggestion of small mountains off to the left against the border; twinkling lights on the plain suggesting towns; the ocean with a glowing horizon suggesting the sun just sank; stars above.

You'd probably have to expand your canvas to do that justice though, maybe have the mountain slightly off-center to the right? Probably extend the canvas left from where it is now, and up a bit too, keeping the mountain bottom right-ish.

Whatever you go with, it already looks fantastic.

edit: if you go that way, the side of the mountain facing us will be in heavy shadow, so maybe put some torches or a lighted trail spiraling up it?