The most traditional article of clothing for your baby to wear on the day of their christening is a christening gown. For some people, dressing their baby boy in a gown can make them uncomfortable, but there is little reason for this, as this is what has been worn during christenings for hundreds of years.
Many families have passed gowns down through numerous generations, with all of them wearing the same gown. Often times, the quality of the clothing is high enough to allow for this easily, as does the point that the gowns are unisex, and can be worn by your baby boy or girl.
You also have an extensive number of options regarding christening gowns, made from quality materials, often by hand, and by some really talented designers. Your other options could include having a bespoke christening gown, where you can design your baby's outfit to your individual tastes.