I also love Atonement. Here are a few suggestions that you might like.
Everyone Brave is Forgiven by Chris Cleave
All the Light We Cannot See by Anthony Doerr
Life After Life and A God in Ruins by Kate Atkinson. Or just about anything Kate Atkinson has written.
Anything at all that Sarah Waters has written. Fingersmith is my favorite (Victorian setting, intricate narrative, many references and homages to 19th century literature), but all her novels are brilliant. The Paying Guests (set in the 1920s) is the one I have liked best of her more recent works.
This may be a bit of a long shot but have you ever read the Flambards books by K.M. Peyton? They were originally written for (or at least marketed to) the young adult crowd, and I first read them as a teenager. But I recently reread the first book in the series and I found it held up extremely well.