I’d guess that since wiring any primary Sonos device has become an option Boost sales are way down as they are so rarely needed.
(e.g. removing the need to have a wired node for SonosNet to work).
That would be quite a networking achievement, I suspect, as the wired link allows the two different wireless protocols (SonosNet and WiFi) to send data to each other. I don't know enough to say with certainly that it's impossible without a wired link, but I suspect that to be the case.
I’d suggest an additional One or One SL
I’d already have one the surround speakers physically very close (1-2 feet) to where I’d need to place the “bridging” One, which would be redundant unfortunately.
A Sonos Boost would also work
Yes. I was looking at the Boost. But very surprised to hear it’s on “last chance”. I’m missing the replacement model too. Are Sonos phasing this out as an option? It would seem to be an odd move unless they have other ways of working around it. (e.g. removing the need to have a wired node for SonosNet to work).
I’d suggest an additional One or One SL, located where it was easy to wire to your Ethernet. Even a used Sonos as long as it is S2 capable would do if cost is an issue.
A Sonos Boost would also work but it appears to be on the way out as it is listed as a “last chance” sale item.
https://www.sonos.com/en-us/shop/boost
According to Sonos:
A Sub, Sub Mini, or surround speaker cannot be used as the single wired product.
https://support.sonos.com/en-us/article/switch-sonos-between-a-wireless-and-wired-setup