Difference between Swiss Pass and Swiss Flexi Pass

Hello George! Great that you're returning to Switzerland after so many years. I think you should do some research first before composing your itinerary. Of course I can recommend places, but there are so many that it helps if you can indicate your preferences (cultural actvities, scenery, landscapes, train rides, viewing points, duration of your stay, plans to stay in one basetown or to travel throughout the country? etc). You could start off with browsing this forum (search for 'travel reports for example to read about other visitors' experiences) and the sections on the Bernese Oberland, Graubünden and Wallis, including the day trips sections. The timetable and hotel overviews may also be of help.

I know of a factory outlet near Lugano (Foxtown in Mendrisio) and in Murgenthal (Outletpark). I don't have personal experiences there though.

The Swiss Pass is described here, the Swiss Flexi Pass here. You've mentioned the most important difference, but note that the Swiss Flexi Pass also grants a 50% discount on non-free travel days and that its validity can be stretched to one month (it's valid from your first up to and including your last free travel days). On free travel days, the Swiss Flexi Pass works exactly like the Swiss Pass.