Use 1 x A2 together with an OCF II Adapter and an OCF Softbox 3' Octa. Use the live view in your camera to help set your ambient to the desired look. Place the flash and softbox on the same side as the natural light is coming from. Put your remote in TTL mode and snap a shot, then flip the remote into manual mode and fine-tune the output.
Pro tip: If you want the image to feel more natural, slow your shutter speed down to decrease the amount of contrast.