I would put only 1 piece but it seems too large to me

Tried putting just one.The wall looks bare to me

A horizontal arrangement or piece would look better and not fight with the ceiling asymmetry.

This is the room without any art on the wall

I don't think the wall looks bare with just 1 piece but I do like the look of nothing on that wall. Your headboard is lovely let it be the attraction

I like the two, just the way you had it. Don’t worry about the ceiling, it’s just a ceiling.

Nothing looks best

Yep no art over the bed looks best. And the accent color is just accentuating the irregular ceiling. I'd paint the whole a very light taupe and do the ceiling in the same color but 25% lighter.

You simply need to redirect the eye. Put black shades on larger lamps to match scale of bed. Put mirrors behind the lamps. A starburst mirror over bed rounds out the look an add small scale chair with fluffy throw for additional texture. Add one pillow to bed to repeat heavy wood interest. The ceiling and asymmetrical situation will fade from view.

You need much more contrast too. Everything is beige and golden oak.

I love it the way it is