Can you help us narrow our suggestions down by providing more info about what you are looking for? Which era? (Romantic, baroque...?) What mood or style?
Maybe a Chopin nocturne? For me Op. 27 No. 1 and Op. 48 No. 1 come to mind. Or if you want another Rachmaninoff, the Elegie or famous Prelude from Morceaux de fantaisie?
Well, they definitely feel less substantial than the Moment Musical. The prelude, especially, is a lot easier than it sounds. You could try something from Schumann's Carnaval - Chiarina and Aveu fun ones that meet your criteria, and are a bit easier than the ones I previously mentioned.