You could opt for a very simple cover. Solid color with a small image of a mushroom, or a crescent to signify the Cheshire cat's smile. A cover can be super simple, but also very striking. They don't always have to be overly detailed or complicated, if that helps 
^This one gives me an idea. You could have your title on the cover look like it's falling vertically to mimic Alice's fall down the rabbit hole. Maybe have like a mushroom or smoke rings or something encircling some of the text.
I'm not the best with design, but those are some ideas if you need something fast so you can post your stuff.
Same for the thumbnail. Simplicity can be hard to achieve (lord knows I am way too detailed and struggle with minimalism), but it's something that doesn't require someone who's not been drawing for years to create.
I don't know enough about your story to know what elements will be important. But whatever you were writing about you could maybe connect with the cover in some way.
Good luck!
*edit is because I said "ellipse" instead of crescent. Oops.
