"Seventy-five years have passed since the British writer died. To mark the anniversary, we commissioned an animation of a BBC radio broadcast she made on 29 April 1937."
Suggested terms to look for include - diary, diaries, letters, papers, documents, documentary or correspondence.
Combine these these terms with the event or person you are researching. (example: civil war diary)
Also search by subject for specific people and events, then scan the titles for those keywords or others such as memoirs, autobiography, report, or personal narratives.