To go into a little more detail:
Regarding noise-canceling headphones: - I find them uncomfortable to wear for really long stretches - They don't fit well when I'm wearing glasses (contact lenses aren't an option for me). - I can't solve the problem by just wearing them sometimes, because I can't guess when distracting, transient sounds will occur. - They don't filter out low-frequency sounds enough to solve the problem.
Regarding sound-dampening materials in the floor above my office: - Likely to help, but not sufficient. Also, we're not ready to put carpeting on that floor yet because of dust issues. (We can solve those eventually, but not quite yet.)
Regarding less extensive soundproofing in my office: - There are just too many pathways for sound to get in currently. - From the research I've done, it looks even a single pathway is enough to let in more sound than is acceptable.
Also worth mentioning that I've got a nasty case of A.D.D., so I probably take longer to recover from minor distractions than many others do.
[1]: https://www.amazon.com/Marpac-Classic-White-Noise-Machine/dp...
Sadly, my kids' sound spectra don't really fit that profile :)