Anne McCaffrey's Pern novels (the original Dragonriders, and Harper Hall--can't speak to the later series written with her son)

I read tons of British/Commonwealth drawing room and procedural mysteries at this age, as well, not only Christie, but

Dorothy Sayers
Georgette Heyer (known more for her period romances, but also wrote quite a few mysteries)
P. D. James
Catherine Aird
Ngaio Marsh
Margery Allingham

also, in other genres

P.G. Wodehouse
Patricia Mckillip
Arthur C. Clarke
Isaac Asimov

offhand.

...pronounced like the long vowel and first letter of the alphabet...