Smart thermostats are all the rage these days, and there are plenty of options for consumers to choose from. If you want something (relatively) inexpensive, you can now buy the Ecobee3 smart thermostat for $199 on Amazon, $50 off the original price.
The main differentiation with the Ecobee is the separate room sensor, which is designed to more accurately change temperatures across your house. The sensor can also detect if a room is occupied, and will de-prioritize the room if it's empty.
The Ecobee3 can be controlled from Alexa, but unfortunately not through Google Assistant or the Google Home. However, you can get the basic functionality by connecting the Ecobee to either IFTTT or a SmartThings Hub, and then connecting that to Google Assistant.