I always wear 'floaty' unstructured dresses in the Summer - those linen M&S dresses upthread are typical of the sort I usually wear. Today I am wearing a HUGE oversized Kin dress that comes almost down to my ankles.
I prefer the look of plimsolls (Converse, Vans, mens Skechers, etc) to trainers, and I usually wear a thin, unlined, preferably unlapelled linen jacket as it is far cooler for the Summer than denim. Today's is denim-coloured as it happens, zip fronted and hooded.
I have been wearing this style forever. I look fucking fab.