2-wire thermostat / controller

[brainwash]

I live in a rented apartment so cannot modify a lot of stuff. I have electrical heating with two analog thermostats. These have a bimetal strip that close a 220V contact that triggers remotely a big relay (something like 480V / 16A). The current that flows in that thermostat while closed is around 20-50mA. Might be 100-200mA, it's been a while since I've measured it.
There is no null connection, just two wires.

My goals are: be able to remotely start/stop the heating, set the temperature digitally, measure how long the contacts stay closed (for power consumption, the heating runs at full power when on). It's doesn't need to react instantly, I think 1-2 minutes is fine.

I don't know if there are similar modules on the market so I was thinking maybe I could parasitically power some RF module that does the job for me. An ESP8266 + triac/ssr would work nicely but it has the issue of power consumption. So perhaps either power it from some batteries for a while and see if the idea works or use a lower-power RF module.
I don't know if the ESP8266 can be held in low-power and with WiFi off while it measures stuff and wake up once every two minutes or so. I'm saying ESP8266 because it has both the RF transceiver and the uC integrated.

Just thinking out loud.

[Seekonk]

This might be worth looking at    sourceforge.net/p/opentrv/code-0/HEAD/tree/trunk/Arduino/V0p2_Main/

[brainwash]

Looks interesting but I'm targeting a different use-case. There's a slew of valve controllers on the market, I'm pasting links from amazon.de but just to show the products are already there:
https://www.amazon.de/SmartBlue-Heizköperthermostat-Bluetooth-Programmierung-Smartphone/dp/B0168RN8ZW/
The innovative thing is the occupancy sensor but it's not applicable to me.

Meanwhile, I'm looking for a replacement for one of these, in the same format:
https://www.amazon.de/Eberle-Raumregler-RTR-GradC-111110151100/dp/B0014DOH0Q

Or, some module I can build myself and attach to the existing one. I would set the cutoff at the main contacts to 30C and use my addon to control the heating.
Or if something similar (same format) exists with RF control, I can intercept the signals, that can also work for me.