Who knows about crepe myrtles?

[domesticdiva]

So, you could say I don't know anythinng about gardening. Ive seen these crepe myrtles everywhere that look more like a bush than a tree. My question is....is that just the way they were pruned or are they just a different variety? I saw some crepe myrtles at walmart and the tag said it grows up to 20 feet tall and 10 feet wide. I don't care how tall it gets I just don't want it too wide. If I bought it, could I just prune it to keep it small? I was thinking of planting full sun plants nearby and I don't want it to get too big and shade my sunny plants. (I was thinking about knockouts or maybe lantana??) thanks for any advice...my clueless about what I'm talking about!