Audio therapy is very helpful -- quiet brown noise in the background can be very helpful for assisting focus.
This is one of my favorites: https://www.youtube.com/watch?v=RqzGzwTY-6w
This is one of my favorites: https://www.youtube.com/watch?v=RqzGzwTY-6w
My solution was a pair of noise cancelling headphones and either really ambient music or brown noise like you mentioned. I've found it to be very effective with helping maintaining deep focus.
I fear that the solution to a noisy office being "add more noise" will cause hearing damage.