Not sure if it counts as bedding. I grow ammi majus to plug gaps. It's white so ticks that box for you. My other favourite is snap dragons😁. Remind me of being a kid.
You might be as well to go the garden centre and make a decision based on what's available! Bedding plants have been selling out incredibly fast at the ones round here.
I dont plant bedding as such but I have nicotiana alata, Californian poppies and love in a mist that self seed. I always scatter some mesembryanthium and sow some calendula and tagetes for pots etc.
And definitely worth trying some white verbenas and calibrahoas. For a more aethereal look, I'd suggest euphorbias, like diamond frost, they fill in gaps very elegantly or great to soften edges of pots.
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I live in west central Scotland - not where that photo is...