I have also been considering this, simple on/off no need for any temperature control, already have that.
I have considered the MiHome Energenie relay around £30 because in my case I already have the hub, there is really no need to control domestic hot water, be it instant or stored as even with stored if no water used the energy loss is so slow it is not worth the effort.
However because of the price of the hub, for you likely not best option. You want a simple wifi light switch that needs a neutral, where in the UK for a light switch we want one that does not need a neutral. I know there are switches made that have a neutral so don't need a drain through the boiler, and don't need a hub. But as to which one will work for you I don't know.
With MiHome Energenie I have eTRV heads which do not seem to have a limit to number of events, however 13A sockets, light switch, and energy monitor/remote switch all have a limit of three events. I would assume the relay is the same. The big problem is a power cut, they default off, so until next timed event it will remain off.
I originally fitted to socket to work an extruder alarm, to warn me if mother went out of the house, the alarm was fitted up stairs to wake us in the night should she wander off, but that meant going upstairs to switch it off or set it, tried timer, did not work as people would come to the door outside hours set for, tried simple remote control, but it did not report state so we thought it was on when it was not, the smart socket combined both so even if not set, next timed slot it would set anyway. Now socket just turns on my bedside light.
Lightwave also do a relay but again it needs a hub. Weton states no hub required, Sonoff also seems not to need hub. In most cases you will likely need an adaptable box to mount it in, the programmer is only a time switch, but if your looking for a simple remove off programmer and replace with new don't think you will find one.