What to wear to informal Christening?

[upsidedown2017]

It's in Sept so potentially warm. Casual affair, not particularly formal. Definitely don't want to appear overdressed. What on earth to wear??

Any ideas? I'd have to buy something new as absolutely nothing suitable in my wardrobe that fits.

Christenings are normally Sunday Best.

If at a very informal church, I'd recommend either a dress/smart cardio combo, or trousers (not jeans if you're not sure of norms at venue) with nice too or she'll/casual jacket

I was thinking casual dress or wide leg trousers but unsure of shoes, so as not to look too OTT