Sorry for the delay in responding - we finally arrived in Sorrento after catching the 17:26 CE and have been able to enjoy some time in Sorrento this evening after 8 hours of train headaches!
We purchased from the official site here:
https://ots.eavsrl.it/web/public/ots/ticket/index
I had tried from the app but couldn’t figure it out, even when I tried to register.
We had originally booked our train to Napoli with a buffer of 1 hr to make the 15:37 and after our train was delayed, we barely missed the earlier CE and had to wait for the 17:26, so we had a 2 hour wait. If we had more time and could have planned we would have taken Letizias advice to store our luggage and go for pizza.
For what it is worth, the Napoli train station was super easy to navigate. We found the campania express ticket windows with ease and when we showed our tickets the worker was confused and said we could take the 17:26..but I insisted he print us new tickets showing the 17:26 time. After printing the new tickets, he told us to come back at 17:10 and wait there by the ticket window. When we did so were about 50 other people and the workers escorted us all down to the platform and onto the train. It was very smooth.
fjj3748 - I, like your wife, did not want to do the regular commuter train my first run with all of my luggage. It was worth the wait but very hot in the station; we took the opportunity to browse the (air conditioned) shops and go upstairs to get a glimpse at Napoli and enjoy the cooler breeze and shade..