Which heater is the safest to warm the room where my newborn sleeps?

Red Nose has the following information about room temperature & heating.
It is not necessary to monitor the room temperature or to leave the heating or cooling on all night, as long as the baby is dressed appropriately for the room temperature.
Dress baby as you would dress yourself – comfortably warm, not hot or cold.
Red Nose does not recommend a specific room temperature for baby’s sleep.
This is because there is no evidence to show that maintaining a specific room temperature prevents sudden infant death.
https://rednose.org.au/article/room-temperature
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep
https://rednose.org.au/article/how-to-dress-baby-for-sleep

It is important to take in to account the use of a heater when deciding how much bedding to use for the baby whether using a heater or not.
Probably using a heater with some control over the room temperature would be preferable.
ensure it is not positioned where baby may have access to it.