I just added some variegated irises; even though the blooms aren't white, the white variegation on the foliage will be nice all year, and some of my floppy poppies can lean on it the rest of the time (hopefully).

I put in some white-flowered alliums, as well as some frittilaria as well. For butterflies, I'd consider Asclepias Ice Ballet, buddleias, maybe beebalm or verbenas? My annual flowering tobacco reseeds every year, I'm so glad I planted it now, those would be high on my list as well.

HTH,

Celene