D..
My infant was in an all white christening gown made out of a 1930's petticoat from way back in the family. Very cool, and very beautiful!! However, my younger son was a toddler by the time we got him christened. He wore a little blue and white outfit, shirt and shorts. It was very cute and fit the bill very well.
Do what you think is best. His outfit wasn't actually hard to find at all, and probably easier because it was spring. Plus, he did wear it many times for nice after that...