At my parents house I made their current Honeywell Chronotherm programmable thermostat smart by using the TELE setting that is available. There are two contacts that when wires are are connected and making contact a TELE setting is activated. It’s possible to set the temperature of the thermostat in the TELE setting beforehand. I used this as an away mode.
Information from the Chronotherm manual (in Dutch)
Video of the configuration:
Webpage that inspired me (Dutch): https://td-er.nl/2015/04/13/bedien-je-verwarming-op-afstand/
Screenshot of the dashboard. I added a DHT11 sensor for temp and humidity.