We've got one to go to in a month. They're regular church goers (rather than people who are just attending for the christening/party, as we did!). Only mentioning that as I wonder if they'll see it as less of a photo opportunity as they go weekly and therefore won't be a dressed up.
I've got a navy jumpsuit-might that work? I'm in my mid 40s, 5ft 2 and a size 10/12.