@newgardener, It's quite a shame that the AC was placed so low on the wall, it would be so hard to sit under it when on, you would get a stiff neck from the cold in no time. It should have been right up below the cornice, then artwork would be simple. If it were me, I'd have it moved up, repair the move and you have your wall back, not particularly an expensive job just a bit messy.

I would suggest hanging a large moroccan woven fabric or mat, just use a length of dowel along the top edge, and hang it up. It would add great texture and also a casual feel to the room. Dress up the couch with a bunch of patterned cushions and a bolster moroccan style. A silky fabric sun filter curtain would finish off the look. https://nz.pinterest.com/pin/299911656409300053/ https://nz.pinterest.com/pin/405675878916401870/ https://nz.pinterest.com/pin/431219733049382426/

Zazzle.com.au have some cool and affordable posters you can then frame with IKEA / KMart / target frames etc... try searching graffiti for something edgy or beach photography for some Cali type images... or there's architecture shots too. There's multiple sizes available and you can then try matching up to frame before purchasing.. Good luck

Because the bedhead is curved, I am not sure that rectangular art will look great...maybe try something a bit different ?