Is that everyone's experience though? We set ours to 18 and only occasionally turned it up to 19 and it was fine all winter.
Today I'm walking around in a T-Shirt when everyone has some kind of thin coats on, but when I sit and idle for an hour, or get hungry, I cool down considerably.
My wife is extremely resistant to heat, but this disadvantages her in normal and cold weather severely. Her baseline is 22-23 degrees C to live comfortably, with long sleeved warm clothes.
Also, temperature doesn't always indicate cold's penetration power. If the air is dry, -18 degrees C is survivable with a mid-thickness polar coat. If it's humid, try to survive 2-3 degrees C with a down / wind-resistant coat. It won't be easy.
The same goes for handling heat and humidity. I grew up with average temps of 35 degrees C in a dry climate. It was not a problem at all. 28 degrees in high humidity I find unbearable.
Also, feeling cold at night lowers my mood, and I don't want to do anything. However, I'm fine during the day when my body's running at its usual. I live with a t-shirt all year round, even.
Adult sleep quality benefits quite a bit from even cooler temperatures at night, ~18.5 degrees C. Use a heavier blanket.
Being tired, not being able to warm oneself after dinner at home because of a slowed down metabolism at 18 degrees C is not comfortable for me (yes, even with warmer clothes, socks, etc. Hot drinks helps, but temporarily).
You're describing something that is true of every human on Earth. Everyone gets cold when they don't move. Everyone's body cools down at night. You don't need 20C to sleep at night.