homeassistant

Sounds like a simple enough job using a DS18B20 sensor on a cable. They're digital ambient temperature sensors with ±0.5°C accuracy, and can usually be picked up quite cheaply.

Aside from GND and 5V, they only use a single GPIO pin. As each one has s unique 64-bit address, you can wire more than one to the same GPIO pin without any issues. The only other thing you'll need is a 4.7K resistor on the 3.3V to the GPIO.

Here in Australia, I got these from Amazon, and wired three up on a single GPIO pin for our lizard's enclosure. I then wrote a quick and dirty Python script that publishes the temps into MQTT four times a minute, and load them as sensors in HA, to do things with. Admittedly, I'm running them on a Raspberry Pi, but that's only because I'm also hosting a couple of webcams on it, to keep an eye on the lizard.

You could absolutely do this with an ESP board - esphome has you covered.

Edit: this tutorial will help you get started on how to wire it up.