You can definitely combine a relay and wall switch with a smart Bulb, but you usually want the smart bulb on a different circuit because ordinarily the relay will cut all power to the bulb. So you have the same problem with SmartSwitch or a dumb switch.
In the United States, it is legal in some jurisdictions, but not all, to have a loop at the switch so that the bulb always draws power. The switch communicates to the hub which then communicates to the bulb and tells it to turn on or off. I don’t know if that’s legal in the UK or not. That said it does solve the problem because you can turn the light off with the switch and the bulb goes off, but the bulb is still actually drawing power so it can hear the next on command.
The battery powered switch option really is the simplest. You can put it next to the regular switch, or in a completely different place in the room.
Many people put a childproof lock over the regular switch as a reminder to others to not use it except in an emergency. These are widely available and generally inexpensive. They often come in different styles. In some cases you replace the whole switch cover with one that has a built-in lock and in other cases you put an inexpensive piece over the top of the existing switch.
So it comes down to decorating style really.
At my house, I am have a number of healthcare workers come in and out, as well as my housemates’ friends, and I don’t care that much about looks, so I just got very inexpensive ones. They cost around one euro. But you can get much more elegant ones.
Here are some inexpensive UK examples. These are typically found in the baby department, but people also use them to keep freezers or Aquariums from being turned off accidentally.
http://www.amazon.co.uk/Switch-switch-prevent-switches-leaving/dp/B00I3GLL9W/
I know you’ve probably already seen this but for those coming first to this topic, the following topic is the FAQ for lighting controls for the UK. So if you did use a switch cover on the existing switch, then the following topic shows a number of alternatives for actually controlling the smart bulb under option 2)