You only
need what plants make you happy. I would recommend going a little deeper on the substrate. Maybe burying the wood a little deeper on the left. Some type of moss would cover that wood really nicely.
Taller background plants would really help solidify the balance, and some lower plants inside of the "cove" of the wood would look nice too. The nice thing about stems is once they get tall, cut them into thirds and replant, it fills in pretty quick.
Your stocking is a little funky though, what quantities of fish do you have in there? I see an angel, a couple neon tetras, glowlight tetras, platys/guppies/mollies, two rainbow sharks (which get territorial), what looks like a cory and a bristlenose. To each there own, but your tetras would like a school of their own species.
I tried a little photoshopping to give you a visual idea of what I am talking about. A 26 isn't that hard to assault with plants.