The comics, but they don't go too far from the end of ATLA, so you won't see anyone dying but at least you can find info about Zuko's mom, the creation of Republic City and what hapenned in the world after the war, in this order:
The Promise (trilogy)
The Search (trilogy)
The Rift (trilogy)
Toph Beifong’s Metalbending Academy (one-shot)
Smoke And Shadow (trilogy)
North And South (trilogy)
Imbalance (trilogy)
There's also a short comic, Clearing the Air, that shows a bit of Tenzin younghood. After TLOK there's two trilogies too: Turf Wars, Ruins of the Empire. I hope you enjoy!
