A painting would compliment the room nicely. One that does not overtake the space but still fills it up

Agreed that a large piece of artwork would be great. Perhaps even a triptych (picture/painting that is in hung in three adjacent panels) or mirror(s)?

Also consider a decorative element like a 3D sculpture. I've attached some images of ways to hang artwork over a bed - not necessarily the right colors, but just to give you an idea. Good luck!

I don't think you need anything at all up there. It's a lovely and very restful looking room just as it is.

The picture included below shows one of our designs for a client. Notice above the bed?