That's the only place where 43C is high.... in your head.
43C is nothing.... and browsing the web isn't the way (a good way) to measure temperatures. You want to test with a more significant load, like a stress test of your choice (maybe AIDA64 or something similar). These chips are good to 100C.
As far as fans, you can add more...sure. Airflow generally helps, yep! The 120mm AIO will be a slight improvement over what you have, but, I'd look more at a 2x120mm or 3x120mm.
Again though, we have no idea what your load temperatures are and 43C browsing the web is fine (albeit a bad measurement method).
EDIT: I see now that chassis is a MiniITX so you don't have a lot of room. If you move to 140mm fans, make sure they move more air than your current ones. Since you can only fit a 120mm AIO there, it is what it is, and it should improve temps (not that you have to with the limited information we have)... but not sure by how much... maybe a couple/few C.