Sounds like you're doing the right thing to me. I assume he's waking up because he needs something, so you just have to keep trying things until you figure it out.
I would change diaper, make sure clothes are comfortable (good temperature), cuddle, sing sooth. Tell him he needs to stay in his bed during night even if he doesn't sleep and you'll be back at day time.
DS would get hungry in the middle of the night at that age, so we'd have to go downstairs and give him almost a full meal in the middle of the night. Whew, if you go there be careful not to make it a habit.