It is impossible to use Alexa on the Sonos One because the Alexa voice volume is linked to the general volume of the device. If you listen to music at 50% volume, Alexa will answer you by shouting (the neighbors will hear it too). If you listen to music at 10% volume, Alexa will answer so softly that you must lean your ear against your Sonos to hear it.
The problem is so evident that I had to buy two Amazon Echoes to use Alexa in the same rooms where I already have Sonos Ones. Yet, even though hundreds of people before me have already raised it, Sonos doesn't give a damn and, for years, has continued to sell Sonos Ones at a higher price because of their supposed Alexa compatibility.