Controlling baseboard thermostats?

So I have a central HVAC system however I have two rooms which have their own heaters controlled by separate thermostats on the wall.

How do I get my hestiapi to control these as well ?

Is the controlling circuit of these heaters located in each room?
Do you need individual temperature reading for each room?

Yes, they are all on their own circuit. One is the upstairs bedroom (the hvac system doesn’t reach) the other is the bathroom which has a supplemental heater.

A heater similar to the bathroom heater is this one
It has a heat level setting and a timer

I’m not sure if it can be set to always one and then I could control it with some kind of high power relay (I assume this is a 1500 watt heater, so that’s more than the average smart wall switch)

In the bedroom, it is a wall thermostat like this one
It drives a similar heater but it has no built-in controls, the wall thermostat switches it on and off.

So I suspect I need a (probably battery powered) wifi temperature sensor in both room. In the bathroom I probably need some kind of smart controlled relay that goes in the wall in series with the heater and I set the heater to on all the time on the front panel.

For the bathroom I need some kind of relay that fits in the wall box with some basic temperature control and sensor that is wifi capable and runs off the 120v.

For the bathroom heater, I guess I could use one of the sonoff product but I would like something with UL or CE certification so I don’t have trouble with the insurance company.

For the wall thermostat, I don’t know of any product that would fit right. Most of them require cloud servers and are meant to be part of some proprietary ecosystem, that’s not really what I want. So if you have any suggestion of products that would do the job and work well with the hestiapi that would be great !

I cannot comment on certifications etc but for the bathroom you can get away with 2 relays tied together. One smart-wifi enabled relay with minimum Amp power that triggers the second relay that can cut loads that the heater requires. The smart one should support MQTT and have a temp sensor. I don’t know of any commercial solution. Would you get away with using a M5Stack one being powered from battery or a certified power brick maybe located outside the humidity of the bathroom? That means of course you would have to run the temp sensor cables too.
Regarding the room heater, it probably also cuts high currents. A second HestiaPi might do but it has the price you know unless you remove the LCD and the case. It will also require mains available inside the box and not just the 2 wires the bimetallic contact cuts. Please check all the requirements and get back to us.