I realise this is a bit late for this year! Just thinking ahead for next summer & in the optimistic hope of a nice autumn.
Winter time I wear boots, knee boots with skirts, biker style with trousers. Summer I have sandals of course then nice canvas trainer-y things which work well with dresses or 3/4 trousers. But I never know what to put on my feet when it's raining but warm.
(I wear leather hiking boots for work more or less year round with thicker or thinner socks depending on weather, so that doesn't help.)