I've just re-read The Making of a Marchioness by Frances Hodgson Burnett. This is one of my favourite Persephone titles. I particularly like Part 1 with its Mitford-esque humour and cast of eccentric characters. Part 2 is a little more melodramatic and certainly darker but keeps you guessing until the end.
I wanted a substantial novel to read for August so I've bought Someone at a Distance by Dorothy Whipple, an author new to me. At over 400 pages, this should do nicely. I'm two chapters in and I like her writing very much.