Wide fit shoes help!

You can often find fairly wide, flat sandals, especially if you go for the toepost ones that give your feet a bit more room.

Alternatively, you could look at minimalist/barefoot styles - these are, by definition, wide and flat. They tend to be more expensive than conventional shoes from high street stores due to smaller production scales, but are cheap compared to a lot of the designer footwear people pick for their wedding day!