Amazon, Apple, ebay, Direct from supplier?
I currently have a homekit setup that includes Hue bulbs, Elgato TRVs, Tado Thermostat, with a homebridge script to extend homekit and allow me to use Harmony Hub, and LightwaveRF.
The homebridge is a bit hacky, so I wouldn't bother if you're not a technical person.
Elgato does thermostats, UK power plugs, Radiator Valves, Weather/Temp sensors, door/window sensors, (they're now adding motion sensors, and wall switches) but they're Bluetooth LE... which means they don't have their own hub... you need an AppleTV (3rd Gen or later) to connect to them outside the house. There's a bit of a delay with the TRVs, so I don't know how well that will translate when using plugs or switches :-(
Homebridge also has a SmartThings plugin, which would let you connect to your Things via HomeKit, which helps to expand the range quite a bit.
