The question you're asking, as it stands, is a null question, because the perspective of your piece as is dictates that there won't be any visible sky in the final piece at ALL. You seem to be suffering from the belief that 'a background has to have a ground plane and a sky plane or else it isn't finished' or something, but this is only true if your horizon line is in the right place! Right now, you seem to be trying to force a horizon line about halfway down your page, but that's CLEARLY impossible because the character on the tree contradicts this. They're ABOVE the horizon line, so that means they're technically in the skyplane, so you should be looking at them from BELOW- but instead you've drawn the character as seen from above!
Remember, the horizon line is eye level. Everything in the picture underneath the horizon line is beneath eye level, meaning you're higher up in elevation than it, but everything in the picture ABOVE the horizon line is HIGHER than eye level, meaning you're LOWER in elevation than it.
I mean, you could also say the character's height is the size of a skyscraper, but that's clearly not what you're going for here.
My suggestion: ditch the idea of a sky and just put a low-importance background of a bunch of trees in vague misty shadow behind the current scene, using the same perspective you've been using for everything here. The work in the foreground is excellent and you'd have to completely trash all of that if you want to make a scene incorporating a skyscape.