We stayed IN the town of Pompei, (one i) 5 minutes walk from the Ampitheatro entrance, not the main entrance. You could take the Circumvesuviana as described by Tod, meet Askos at the main entrance to the Pompeii scavi (you need to walk up a hill to the entrance) and go from there. But I'm sure they could design exactly what you need if you really wanted a driver to pick you up in Naples. I found Askos very helpful by email on their website, they got back to me within a day or 2.
I can't imagine doing Pompeii, Herculaneum & Oplontis is one day! If you have time, do Pompeii in one long day, the others another day. I worked out walking in a pool & doing PT for 6 months to prepare for the rough walking!! hahaha (I'm in my late 60's.) We wore Merrill Moab 3 hiking boots & I had walking sticks, I was the only person I saw who had them, gosh what a help they were. That overhead walkway inside Pompeii where you get to gaze into the ruins was a peak life experience! I hope you have a wonderful time.