In my search for better whip antennas I ordered some from RS Components. The first one is:
https://za.rs-online.com/web/p/telemetry-antennas/0542563/
This antenna resonates at 885MHz, a little higher that promised. But it is also quite wideband, so even at 868MHz the S11 is very low. So this antenna performs good enough for an end device.
As an aside, this antenna also resonates at 1900MHz, saying that it might have been designed as a GSM antenna, but later tuned for 868MHz.
This SWR at 868MHz is 1.2, which is very good.
Conclusion
This antenna has acceptable performance for end devices. I will not use it on a gateway where I do not want to receive unwanted signals.