Hello Paul , for factual accounts
I find Lyn Macdonald`s books very informative,The Somme
They Called it Passchendaele
To The Last man.
Robert Graves` classic ,Goodbye To All That.
Martin Middlebrook, The Somme.
Richard Holmes, The Western Front.
Vera Brittain`s War Diaries
Testament of Youth.
For fiction-- Sebastian Faulks`Birdsong.
John Harris` Covenant with Death. Pat Barker`s Regeneration trilogy. Viktoria. ,