Wedding wear advice needed

Crossing the Blues, University of the Nations, Social Work and Education, Shop Clothes Online, Radiology Information Social Work and Education This could be an ongoing series of posts until about August but here goes with the first. I am going to one wedding this year, which is the wedding of my sister-in-law. It's an English summer wedding where I've been asked to do a reading. So I need help with what to wear. Here is one of the options I've found, not tried on yet but think it could perhaps work. Although is it too casual and maternity wear like?

Dress and Image from

Any ideas for places to look, I've already tried Liberty and Reiss to no avail. English or London shops and ideally ones where I can try it on! I'm still not very good at internet shopping!

So then I should give you some criteria so you can help me with my search :)
  • Colourful
  • Strapless or one shouldered
  • Possibly maxi but not for definite
  • Weddingy but not too dressy
Am I perhaps just too fussy?! Any and all help so much appreciated!