I'm desperate to find some mod that makes sims not live forever.
Any help would be greatly appreciated!

Your question inspired me, so I've made a new mod. It has two options: it can either kill your sim immediately, or you can play Russian Roulette, which gives your sim a 25% chance of death.

The Grim Reaper doesn't come, though, because your sim doesn't die in the usual way; instead they're turned into a Skeleton Maid. You can either use the maid to clean your house, or you can sell the coffin/maid's cabinet for the usual sum.

I've posted about the mod here: https://modthesims.info/showthread.php?t=679362.

Have fun!

Thank you so much for sharing your mod, you are a life saver!
I absolutely love random chances in the game so having the Russian Roulette option is great.
I can't wait to try this mod!

You're very welcome; have fun!