How to make isolated bathroom towel radiators smart?

[Holdestmade]

I’ve done similar (with metal flush box though).

Replace you single backbox with something like this:

https://www.tlc-direct.co.uk/Products/MKK2025.html?source=adwords&ad_position=&ad_id=415703895087&placement=&kw=&network=u&matchtype=&ad_type=&product_id=MKK2025&product_partition_id=889135910870&campaign=shopping_switches_sockets&version=finalurl_v3&gclid=Cj0KCQjw09HzBRDrARIsAG60GP9rg29N-ghkBpLgjCtXixGuUBIuiZTGswK4S82sYra6Fpgh89b41NQaAoS6EALw_wcB

And fit an unswitched fused spur in one side

MK Logic Plus 13A Unswitched Fused Spur & Flex Outlet White - Screwfix

and a switch and sonoff in the other side

MK Logic Plus 20A 1-Gang DP Control Switch White with Neon - Screwfix

Make sure the sonoff is rated for the load:

Be safe with the Sonoff

Thank you everyone for your replays. Next time I will be more careful what I’m connecting. I think for every device is better to run it on 50% load max, just to be safe.