I can't give a definitive answer but I'm also in the UK and have the same problem. I have been unable to find anything like this so suspect they don't exist.
Possible alternative solutions are...
- Make it a little harder to use the 'dumb' switch with a cover
These were both found by searching for 'switch cover'. These are usually designed to be easily circumvented in case you need to really turn the light off. If the Zigbee switch is nearby people will hopefully take the hint and use it.
You can also get zigbee switch mounts that hold the zigbee switch in front of the dumb switch, you'll have to find the right one for your switch. This is what I have:
Again these often make it easy enough to use the dumb switch if you need to (in this case the zigbee switch is held on by magnets, you just pop it off and use something to poke the switch behind).
- Don't use zigbee
Shelly make wifi switches that do what you want. They sit in the back box behind the switch and can be wired up to take the dumb switch as an input. There are options for if you don't have a neutral but it does get a bit more complicated. There are several products depending on what exactly you need.
I mention this specific company as its the only one I know of that allows you to use a 'dumb switch' as input. I have one of these but haven't installed it yet.
You would use this with normal lightbulb. They seem to have the usual integrations including Alexa.
The only downside is your switch would act as a toggle so you wouldn't be able to tell by looking at it whether it was on or off. I suspect most people wouldn't notice.
Depending on what sort of home automation / IOT setup you have this may or may not be suitable. I have a central hub (Home Assistant) that allows me to mix and match different products but that's all fairly involved.
Sorry I couldn't give you a simple solution but these are the alternatives I've come up with for my own use.