How to keep velocity and add onto it from any rotation.

I’m trying to make a movement system and I need some guidance on how to have a Vector3 that can add onto another one, with rotation accounted for.
Example: If I am moving forward on the X axis at 1 m/s and look up, I still want to move forward on the X axis 1 m/s, and then I want to be able to look in a different direction and be able to move there, while still having all the normal velocity.
Found Answer: Rotate a Vector3 direction - Questions & Answers - Unity Discussions

I would have your camera as a child object of the one getting the velocity applied. Either that or you can look into using global position, so your rotation doesn’t effect it.