You either need a few massive balloons, or hundreds of small ones, and they have to be filled with helium. Anything else starts to look like a slightly sad children's party.
We used giant white ones at our wedding, and I'd recommend looking on Amazon and eBay to find the best deal. To save money, buy helium from party shops like Party Pieces or Argos, and fill them up on the morning of your wedding. Pimp your balloons with fancy strings....for inspiration check out The Giant Balloon Company or buy them from Out of My Bubble.
Blush Pink Wall Decoration by Belle Epoque Co
For more wedding ballon ideas, check out our Pinterest board.