nah, I really don't think it is possible to overdress a baby at their own christening (IMO at least). well, unless they have all frills on their heads too maybe.
and thinkof the gowns that are tradition......waistcoat and trousers is almost naked after the flouncy type of gowns on offer.
also, DS1 was 6mths being christened, in waistcoat and trousers......and looked so nice, and DS2 was 11mths but really really tiny (in fact DS1's outfit was too big on him), and he looked scrummy too. once they were christened tho, I did takae off their waistcoats and leave them just in tiny shirts......far easy and less hot for them.
I put my ds (6m at the time) in a pair of white dungarees he'd been given and had never worn (baby + white clothes + weaning = lots of washing). With a white t-shirt underneath. Then he got wrapped in a white blanket as part of the service.
When we got home i changed him into something "normal" for the party - I wanted to people to see his trendier clothes too <<sad>>
My ds wore linen trousers with a white collared t shirt and like white cricketers tank top over it - was from next as a christening outfit but more like smart wear - he wore a bright green bumgenius nappy as well which shows through his trousers on all the photos