I am elderly and use an electric wheelchair. What I do is google "accessible name of city", for example accessible Naples. I then contact the agency and describe my problems, wheelchair, desired tour etc. I have found many excellent tours this way. In Naples we used "Rome in Limo" for a tour to Pompei which was excellent. Santorini is a tender port. When we were last there I could walk a little. We took an accessible tour that went to a different dock from the normal one. The bus went all over the island and had a guide. The only problem was transferring to the tender and climbing the steep steps into the bus. I could not do either of those today.