I would consider any variation of the rooms colors in a solid a stripe or a print. Solids seem to be on trend now.

Because the color of the sofa looks like a primary color shade of green, I would look at a Royal blue or sapphire blue chair. The white modern coffee table along with the mustard colored pillows is wanting my eye to see a primary shade of blue. I would stay away from any more green unless it si spot on with the green of the sofa.

I like this chair - comes in black/white houndstooth! Click on More Info:

Fabric Upholstered Accent Arm Chair, Eiffel Steel Legs, Denim Blue · More Info

I agree with everdebz, you may want to look for chairs that aren't too square in shape. A little whimsy for occasional chairs are always a nice contrast to sofas, especially sofa sectionals. Plus you also have a very rectilinear coffee table. These are a couple of chairs that add a little flair:

I'd build it up with charcoal or gray given you already have so much color there. I've superimposed my artwork so you can see different colors close to it.

Unless you want to go full green/yellow/gray...

https://www.etsy.com/shop/shoagallery

You need something bigger and placed better over the sofa back

Art!