I would echo lots of what glammanana has said.
I looked online in general. Particularly Jacques Vert[expensive, but they generally include hat, bag and shoes to match if you want it all]. And Phase Eight. I found the hat great, the shoes a bit optional, and the bag not that essential.
Agree about colour scheme, you might even want to take your future dil with you when you shop. Or someone else whose opinion you value. Or go on your own first, and then take someone for some confirmation. I found that the ladies in the shops were helpful, but sometimes they disagreed with each other!
Soooo agree about the heels. I bought the ones that went with the outfit. And they were fine in the shop[ie the 20 minutes they were on my feet].
But longer than that, ouch. I had to take them off at opportune moments during the day.
I went to a couple of wedding fairs, where there were some dress shops in attendance. Some of the bigger stores have personal shoppers[not sure if that is their right name]. I didnt end up using those stores, so cannot comment about how helpful they are.
Some of the intividual boutique stands there did comment that their new stock for the year comes in in January.
I think that other stores stock come in a season or two ahead, so eg now stock would be for spring?
Take time looking online, and have fun!