I can't see the A447 you mention. We rode the A435 from Merida to Huelva a couple of years ago, which is to the west and parallel to the main road between Merida and Seville. It is now one of my favourite biking roads. The road just twists and turns, climbs and dives throughout the beautful Andulucian countryside. Nothing extreme, just 3rd/4th gear, relax, let the engine do the work and enjoy the scenery.
If you think you are too small to make a difference you have never spent the night with a mosquito.