This is something I've been eyeing for the same use case: https://www.getzooz.com/zooz-zen15-power-switch/
Ive had great experiences with Zooz products in general, but haven't used this one (yet).
It does also control, but I'm sure if it's anything like their wall switches it has a setting to default to ON.
EDIT: Didn't see the ZigBee part of your post. Adding a z-wave dongle isn't too difficult if you're open to it. ZigBee sucks IMO.