If you're looking for a place to do laundry and get some work done, then this is definitely the place for you. This combined space has one area for self-service coin laundry, and the other half is a cafe serving food and drinks. Laundry is available 24/7, but the cafe space is only open from 10:30 - 18:00.
It's located in the outskirts of Tokyo in Mitaka (about a 20 minute train ride from Shinjuku) and then a ten minute walk from the station.
Tip: you can check the status of all the machines on this website so you can gauge how busy it is. I think weekdays are probably the best time to go, but even on a Saturday afternoon it wasn't particularly busy.