Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. As you can see I didn’t find any active coupon for this product right now…
Link: Banggood product page
Price: -3 USD
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGEU309, 6GSGIT, BG9b9f60, BG816295, BGd7d9d4, BGec0cd2, BG8f3212
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Heatcold TH123 Smart Thermostat Silver.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).