I am surprised no companies offer noise cancelling headphones for staff. They are relatively cheap (compared to restructuring an office building) and could increase productivity a lot for some people.
Those headphones only block constant background noise, not conversations. In order to do that you have to put your hearing at risk with enough actual noise to overwhelm the rest.
I have tried some decent quality ones. They don't block out conversations completely, but it does sound a lot quieter. They are definitely an improvement over not wearing them.