One of the easiest ways to add some smarts to your home is to replace your standard thermostat with a fancy new one from a company like Ecobee or Nest. These devices can be pretty spendy, but the Ecobee4 is on sale at various retailers today for $199.99. That's $50 less than the standard price.
The Ecobee looks like a small black squircle on your wall. It operates like a regular thermostat if you want to walk up to it and press buttons, but there's also an app that lets you control the Ecobee from anywhere. In addition, it works with Amazon Alexa and just recently gained support for Google Assistant. It also has IFTTT, HomeKit, and SmartThings support.
There are a few different versions of the Ecobee, and the version on sale is the more powerful Ecobee4. This model comes with a remote sensor and has its own mic and speaker for voice commands. It should work with most home heating and cooling systems. The sale price is live on Amazon, Best Buy, Home Depot, and Lowes. There are probably other retailers with the same deal today as well.