for incorporating 'cheapish' bluetooth ble temp/humidity sensors into a Pi solution check out.
https://zsiti.eu/xiaomi-mijia-hygrother ... pberry-pi/
for a wall based temp display and target temp controller consider re-using an old redundant mobile phone you can use to browse to a dashboard web page hosted on your Pi, turn off its screen saver and hook it upto its charger 24/7 == instant HIVE type display.
Host a mqtt broker on the pi too and you can use a wifi/mqtt controlled power relay device to control the heating wirelessly from the PI with control inputs (temp target setting) from your phone/gui
for a control system you can also host on the pi check out openhab, domoticz, or node red.