My daughter painted all walls in her two bedroom house one color. It makes a small house look so much bigger. Take a look at the BM OC colors. There are so many wonderful off whites. One of my favorites is Collingwood.

Sophisticated start. You could go with black and white photography, architectural pieces, art pieces- anything you love on the wall. Then, add pillows in the colors of the art work. If you want to stay more monochromatic, think in terms of textural interest, such as a shag area rug, pillows with seam detailing, etc.

Did you end up painting the ceiling all the same? That's what I would've done!

The market is full of tropical/botanical art at the moment which lend themselves well to tropical or beachy looks. The look you are after calls for natural textures with a soft colour palette, think linen bedding and layer it up with throws and cushions for texture and pops of colour. In my opinion drapes are not a good option in your room as the ceiling slopes to just above your window at a certain point. This would dictate the height at which your drapes hang and, in this instance would be too low. To soften the windows, I would have a tall palm or Fiddle Leaf Fig tree in wicker basket. It also looks like you have the space for a chair.