Probably the Popp sensor is the best you can get with Z-wave. Special note, it can also be used as alarm (you can trigger the siren). I have seen Mertens smoke sensors with z-wave, but I don't know if they share there device specifics to others.
I can only find the "Smoke Sensor / Siren (004001)" Popp sensor for ca. 70 euros. And that is without an "optional AC adapter" that costs ca. 20 euros. I bit more than I am willing to spend on a smoke detector.
The nest is even more expensive, but it does include CO detected which is great. Something to think about.
Be aware that since CO is heavier then air a CO sensor needs to be installed low near the floor, where a smoke detector needs to be installed high.
Any tips for a Domotica proof separate CO sensor?