Very basic analysis.
For you to feel a cold draught coming in, an equal amount of warm air has to be lost.
The outside feels the warm air you lose - you only feel the cold air that replaces your losses.
Very often the cold air you feel on one side of the house is because of the warm air you are losing on the other side of the house... or upstairs... or through the roof.
A case of air flow - invisible but invincible - the front door is more likely to slam if a rear door is opened or vice versa.
Warm air rises, cold air falls.
A misted up mirror/window clears from the top down.
A mirror on an internal wall will clear quicker than one on an external wall
A high mirror more quickly than a lower mirror.
Insulating a wall above a thermostat, especially on an external wall IS a benefit. The reason being if not insulated...
Warm air rises, and collects at ceiling height.
When contacting the wall it cools and drops down when it reaches the thermostat.
It's colder than the room air temperature.
It turns on the boiler unnecessarily because "it" thinks the room air temperature is low.
It's only the air adjacent to the wall that is cooler (the air falling on the thermostat)
Insulating the wall above reduces this unnecessary waste, plus wear and tear of the boiler cycles.
Even a shelf above the thermostat will help.
This logic can be applied to cold air coming through from all parts of the front door.
If the thermostat is situated near to your door, the cold air falls onto it and kicks the boiler unnecessarily into action once again.
Insulate around the door
Use a draught stopper
Ensure no obstruction of mail delivery so that jamming open of the letter box is prevented.
If your letter box is noisy, then you are losing heat and energy.
One solution that could be considered - here