We did last year. with my big bro who is nearly 85. We took a pass for any 6 days travel, in 15. Unlike the old days though, you have to book trains, date and time and seat, for many trains. Although we didn't have to in the old trains in Slovenia.
Not sure if you can include EuroStar. Journey to Paris is brilliant- you have to check in as for a plane at St Pancras. Arrive at Gare du Nord, which is close to the Marais District we like-( we stay at Citadines Hotels, very reasonable and they have quite a few in Paris only). To go to Switzerland, you take the TGV train, quite a few depending on your destination. Where are you aiming for in Switzerland? Different TGV (fast speed) trains go to Geneva, Lausanne, Bern, Basel, Zurich ...
To go to Portugal from Switzerland is quite far, can make stops in Bordeaux and Madrid. AGain, depending where you are going to in Portugal Porto, Lisbon or the Algarve.
Look at the amazing site, the man in seat 21.