A Sonos Roam could be an AirPlay 2 target, and be ‘grouped’ with other Sonos speakers. Likely the least expensive option, although I don’t track the IKEA offerings. 

I see you own at least one Connect and Connetc:amp, some ogf which can only use the S1 firmware (the white app). The question arises if your system is using S1 or S2 firmware? The Roam, as suggested above, will only work on S2, meaning it can’t group with S1 speakers.

Ah, good point, I didn’t key in on ‘legacy’ meaning S1, I assumed it meant ‘existing’. 

If it is S1, then there are many more challenges, as @106rallye suggests. 

The cheapest AirPlay 2 device I’ve seen is an old Airport Express (model A1392) which you can still find very cheap for sale on sites like Craigslist (just saw one for $30). These devices have an 3.5mm analog/optical output jack which I believe you should be able to connect to your Sonos Connect using a special 3.5mm to optical cable.

So this would allow you to AirPlay 2 music from say your phone to the AirPort Express device which then routes the music out to your legacy Sonos system via your Sonos Connect.

Music App on Phone > Airport Express > Sonos Connect > Legacy Sonos System

However, if you’re then trying to synchronize the music you’re casting with other AirPlay 2 speakers at the same time though, I have no idea out how well they will sync with your legacy Sonos system though because the passthrough to the AirPort Express and then wireless sending from the Sonos Connect to your Sonos system might cause some lag. If your Sonos system is all network hardwired though, I don’t think you’d notice any lag in the music syncing.