As others have mentioned, I’d suggest the following options (with links):
- Sonoff S20 ‘smart’ sockets are very cheap (1/3 the cost of Z-Wave sockets), and work well
- Replace the default ‘cloud’ firmware with Tasmota to support MQTT and to give more options. This needs a USB serial cable and some trial and error, but the result is excellent.
- A pre-configured version of OpenHAB for Raspberry Pi with lots of extras
OpenHABian works out of the box, however installing Tasmota and configuring MQTT take a little research. The effort is worth it, especially with the option to build you own modules using £3 ESP8266 modules and Tasmota for sensors, switches, and displays.
As a start, get a RaspberryPi, install OpenHABian and explore the web interface. After that, you can pick any protocol (Z-Wave, MQTT, Zigbee, Ikea’s own, etc) by adding software or a USB interface.
For more detail, there’s several threads in this forum about avoiding using ‘someone else’s computer’ otherwise known as ‘the cloud’. These options all include direct local control from device to controller.