Given your status as a self-described "absent minded professor," you're going to LOVE a Swiss Travel Pass. Nothing to remember except the pass itself (don't leave your hotel without it). Just show your pass (and if asked, your passport) whenever tickets are checked.
Just one potential problem for you. You have to remember for any trips that are not 100% covered by the Swiss Travel Pass, you must buy tickets BEFORE boarding! After days of not having to think about buying tickets, you may forget. You show your Pass when you buy the tickets, and they apply the appropriate discount (25-50%).
Here are some trips you will need tickets for BEFORE boarding, that you are likely/recommended to take:
The trip up the Jungfraujoch (it's covered as far up as Wengen, but the trains go direct from Lauterbrunnen to Kleine Scheidegg, so unless you want to get off, buy a ticket, and wait for the next train, make sure you buy the appropriate ticket in Lauterbrunnen).
The cable car from Wengen to Männlichen (to start the Männlichen to Kleine Scheidegg walk), and the train down from Kleine Scheidegg to Wengen (from Wengen further down to Lauterbrunnen is included).
The funicular from Mürren to Allmendhubel.
The trip up and down Mt. Pilatus. Note that the trip from Luzern to Mt. Rigi and back is fully covered, by whatever combination of boat, train, and cable car you choose.
When you buy the Pass, you will get a copy of the Swiss Synoptic Map. Anthing on it that is a dashed line rather than a solid one, is not 100% covered, and you need a ticket before travel. If you want to study the map beforehand, here's a link to the PDF: https://www.mystsnet.com/fileadmin/doc/02_Produkte_Services/01_Swiss_Travel_System/02_Ueber_das_Swiss_Travel_System/UEbersichtskarte_Synoptic_Map_2018_low.pdf
When looking for what is and is not covered, be sure you are looking at 2018 information - it does change from year to year!