Help with my itinerary please.....

Assuming you are flying back to North America direct from Zurich (not changing planes in Europe), spend the last 3 nights in Luzern. There are direct trains every hour from Luzern to Zurich airport taking 1 hour, so if your flight is in the afternoon like all direct flights to North America, Luzern is just as convenient as Zurich.
Take the train from Zermatt to Luzern via Interlaken for a scenic train ride. You could even stopover there for a couple of hours. No problem doing stopovers with SBB, as tickets are good for any train on the route that day and there is at least one train per hour on all lines.

PS. Are you using a Swiss Transfer Ticket?

I agree with Sam, Luzern is a good choice for all 3 nights. Boat trips on the lake, or just chill out. Take the route via Interlaken and the Brünig Pass line.
Panorama of Luzern: http://tour.luzern.com/360/en/

The Swiss Transfer Ticket has been discontinued, no longer sold.

Thank you both for your replies! Luzern was also suggested by two other friends that have visited. Interlaken was also suggested, so I like the idea of a stopover (if we can secure our luggage at the station?).....

I have been looking at the SBB train app quite a bit. It looks like purchasing a Saver Day Pass in advance for the big train rides (Zurich to Zermatt and then Zermatt to Luzern) make sense and then for our trip to Zurich, simply buying a regular ticket.

Thank you for your help and I welcome any others, this direction has re-energized me!!!

Sarah you can take look at these 2 airbnbs in luzern for your 3 nights

https://www.airbnb.com/rooms/8282909?location=Lucerne%2C%20Switzerland&adults=2&check_in=2019-03-13&check_out=2019-03-16&guests=1&s=a8cpZ8JE

https://www.airbnb.com/rooms/6797815?location=Lucerne%2C%20Switzerland&adults=2&check_in=2019-03-13&check_out=2019-03-16&guests=1&s=a8cpZ8JE

Thanks RJean! Interestingly enough, I was looking at an apartment owned by the same person in your second listing. He has great taste! The first one isn't available during my stay.

No question, spend the three days in beautiful Luzern. Watch for clear skies and then consider one of the trips to the mountain tops. I did Rigi. This gets you a lovely boat ride across the lake to a small town (Vitznau) where you take a cog train to the top of the mountain for lovely views. Rigi is included in the Swiss Travel Pass. Luzern has beautiful scenery, buildings and bridges.

I think that we are going to spend all three nights in Lucerne and then leave from there and go directly to the airport in Zurich. It looks like Lucerne will have plenty to offer us!

Supersaver tickets are train specific, so if you did do a stopover in Interlaken, you would have to specify how long you would be there.

The OP did inquire about a Swiss Transfer Ticket in November. They could still be bought in 2018 and used in 2019, but as Chris pointed out, the time to buy one has passed.

Sam, you are correct that Supersaver tickets are no longer available for purchase and that they were train specific. It does look like they are offering another option that will work for me: Saver Day Passes.

https://www.sbb.ch/en/travelcards-and-tickets/tickets-for-switzerland/1-day-travelpass/saver-day-pass.html

I have been playing with the app, and it looks like buying the pass for my two long days of travel will be most cost effective, and I will save a good bit of money. I do need to buy them in advance and I can, because those days are available for purchase (March 1 and 5). I am trying to decide if I want to purchase first class. Even with buying first class, I am still saving money over buying regular second class tickets, so, hmmmmm......

Then, for my last train trip, Lucerne to Zurich airport, it makes sense to just buy a regular ticket.

I had been looking at the Supersaver tickets and was dissapointed to learn that they were no longer offered, but honestly, I think the Saver Day Pass is going to be great. You can go on most any train, and because it is a pass, if we decide to stop for a couple hours somewhere, that shouldn't be an issue. Please let me know if anything I said is incorrect and I hope this helps somebody else!

Supersaver tickets are still available, but the Saver Day Pass is a better deal. Looks likes 52 CHF pp vs 129 CHF for a full fare 2nd class ticket.

Think about how you will pay for them, as prices go up as you get closer to your travel date. SBB is tricky when using credit cards these days. People have reported good success when purchasing through the app. Otherwise, American Express usually works. Visa or Mastercard may require you to register with Visa Checkout or Masterpass so you have a 4 digit PIN to enter when prompted.