Bedrooms are about rest, so steer clear of anything punchy or zingy. You want colours with a bit of grey in them — muted, slightly soft, easy on the eye when you're half asleep. That's the whole game.
For calm and cocooning, Farrow & Ball Mizzle is a cracking choice — a soft green-grey that feels gentle in almost any light. If you want something with more depth for a sleepy, enveloping room, Farrow & Ball Pigeon or Treron both wrap a bedroom up beautifully, especially with the lights low in the evening.
Prefer warmth? Farrow & Ball Setting Plaster is a soft, dusky pink that reads as a warm neutral rather than anything girlish — it's flattering and restful, and it looks lovely on a north-facing wall. For a quieter, paler option, Little Greene French Grey - Pale is a soft sage-grey that keeps things light without going stark.
The "but what about" here is usually whether dark colours make a small bedroom feel poky. They don't — dark, enveloping colours actually work brilliantly in small bedrooms because they blur the edges of the room and make it feel snug rather than cramped. Hague Blue, Inchyra Blue or Studio Green in a small box bedroom can look properly luxurious. Just commit and do the ceiling too if you're going dark.
Whatever you pick, always test it on the actual wall — bedrooms are heavily influenced by morning and evening light, and a colour you love at 2pm can look completely different at 7am. Paint a big patch on more than one wall, live with it for a couple of days, and check it under your bedside lamp as well as daylight.
Finish-wise, a flat or matt emulsion is right for bedroom walls — it's soft and forgiving. Save the wipeable stuff for bathrooms and hallways.