Buy a 2x8GB kit and replace both sticks.

Trying to find an exact match for your existing 8GB stick is a gamble. Even if it’s the same brand and speed, timings and voltage can differ batch-to-batch. You might get lucky, or you might get random crashes.

A matched kit is cheap insurance. It guarantees dual channel works smoothly, and you aren’t stuck with one stick that doesn’t play nice. 2x8GB is the standard upgrade for that laptop, so just go that route.

You won’t save enough money hunting down a single stick to make the headache worth it.