First of all welcome to Riviera, I hope we'll be able to help you out here on the forum. I'll try and answer your questions in order:
- November is generally quite a pleasant time to visit Portugal, with the November temperature averaging highs of 17 degrees C in Porto, and 13 in Salamanca.
- there 2020 dates for the solos only Douro cruise are already on sale, though they are also for November departures.
- however we also have 2 departures this year, on the 2nd and 9th of August, on standard Douro cruises where we have a reserved number of cabins for sole occupancy at no single supplement. Whilst the cruise will not be exclusively for solos, there will be a group of solo travellers aboard who will be seated together and go on shore excursions together.
I hope that information is of use, and if you have any further questions please do not hesitate to ask.