Grow up?
In regards to the OP - I always have this problem. If you avoid heroics and PvP and space you'll be close to on-level, though.
On one of my alts at the moment I only did class+bonus and am almost level 24 on Taris. So, Nar Shaddaa will mainly end up being class quest and a heroic 4 or to. Still, it's much better than having gaps of quests, I think. Just skip side quests - only an issue for OCD completionists I think.