Yeah, take a look at the Op.64 Waltzes. You've already done the Minute Waltz, so balance that out with the other 2 from the set. Do the C# minor first, though, then the Ab major.
I don'ty like the idea of learning just a few of the Op.28 preludes. They're much more connected than you might think. Some other possibilities, besides what has been suggested:
-Nocturne Op.9 No.1 in Bb minor: Fantastic piece, much better overall than 9-2. The melismas can be whores, though, if you've never played that kind of Chopin writing.
-Polonaise Op.71 No.3 in F minor: This may be a little stretch for you, but it's a great piece and it's almost never performed except in the complete Polonaises studio CDs.
-Prelude Op.45 in C# minor. This is an absolute gem, and unlike the Op.28 ones, it stands on its own.
-Lastly, if none appeal to you, go through a book of the Mazurkas and pick a few. They're underappreciated, and wrongfully so, because many of them are wonderful. Pick a few that you feel confident you can play, because they range from pretty easy to fairly difficult.
Phil