We never jumped into the whole wall decal/art trend ourselves. But when you start thinking about having kids, suddenly you really want to add those touches of whimsey and wall art seems like a great way to do that. Cookie has some tasteful and fun options like this Genuine Fake Bookshelf wallpaper by London designer Deborah Bowness.
You can take a digital picture and just email it to Murals Your Way along with the dimensions you want, and you'll have a personal mural like this one.
Add some texture to your wall by draping fabric like this one from Marimekko. All you need to do is mount a wooden dowel on the wall to create this wall curtain.
Painting color blocks like these is probably the most affordable way to add that flourish you're looking for. We bet you could even do it with those sample sizes if you wanted.