Thermostat with temperature sensor for Boiler

What country are you in? The device selection does vary.

Also, do you have a smartthings/Aeotec hub, and if so, which model?

Meanwhile, take a look at the following FAQ, it should have some candidates for you. The DS18b20 is an external source in this context.

Devices that work with DS18B20 Probe sensors that have working Edge Drivers (2023)