The Era 100 is the upgraded speaker that replaced the Sonos One, but you may find Sonos Ones still available at some outlets near you, or online, so just add one (or more) of those to your room, as required.

Note a Sonos One/OneSL can be stereo paired, or grouped, with your existing speaker, whereas the Era 100 can only be grouped with it, but that can be stereo paired with ‘another’ Era 100.

Thanks Ken

Very useful information.

Tony

One SL is still available from Sonos as a refurbished item.  $159

https://www.sonos.com/en-us/shop/one-sl-b-stock-shadow

Amazing answer