Paris to Zurich, Zurich to Interlaken, Switzerland to Milan

Yes, the TGV Lyria is the best way to travel to your first connection point in Switzerland. If your destination is Interlaken (or up the valley to Lauterbrunnen or Muerren), then Basel is the usual connection point, not Zurich. Buy the Paris-Basel TGV ticket as soon as possible for the best price; such as at www.capitainetrain.com.

You can buy any type of Swiss Travel Pass or Half Fare Card at staffed stations in Switzerland, including Basel. One of those two options will be a good deal and will work as far as the border in any direction. That will be easier to determine the more the plan gets firmed up, but your two mountain side trips are expensive, so you would want a discount on them.

To see the fastest train schedules and connections between any two towns, try the DB train schedule link and tips for using it at How to Look Up Train Schedules and Routes Online.

Timetable for the Paris - Switzerland trains is here: http://www.tgv-lyria.com/sites/default/files/pdf/BROCHURES_CO/TIMETABLE-2016-ch_fr-TGV-LYRIA-EN.pdf
For times of trains in Switzerland go to SBB (Swiss Federal Railways) site: www.sbb.ch

If you decide to get a Swiss half price card, or another type of pass, buy it before you get to Switzerland, or at Basel. That way you can get a discount from the moment you cross the border. If you want to go to Interlaken, the quickest way is to get off the Paris train at Basel, and get a train from there direct to Interlaken. Basel --> Zürich --> Interlaken is doubling back on yourself, look at a map, or just go to www.sbb.ch and enter Paris to Interlaken and it will automatically find the quickest route.

Switzerland to Milan - Just go to www.sbb.ch and enter Interlaken (or whatever your last stop in Switzerland is) to Milano Centrale, and it will again find the quickest route.

As to whether a half price card (halb-tax Abo) or a full pass is worth it, it is best to start a spreadsheet with all your proposed trips listed, and two columns, one for full price and one for half price. You can then price up the two options. www.sbb.ch gives prices.
Note, there is no discount on Swiss Railways for advance purchase (unlike the TGV from Paris), and reservation is not needed.

In addition to the excellent advice from Laura and Chris, look at the passes in the Berner-Oberland/Jungfrau Region as well. You can get a discount on those passes with your half-fare card and by buying a pass you get to ride most of the lifts in the area free, although there is a surcharge for the Jungfraujoch and Schilthorn. As mentioned, you have to do a spreadsheet with what you think you want to do and then do the math.

Chris is correct. If you need or want large supermarkets, a sex shop, fancy large hotels, fancy jewelry stores, or a "Paksitani" restaurant (that's what the sign said, like Punxsutawney Phil), or if you have an aversion to being right at the Swiss Alps, stay in Interlaken. Otherwise, stay right at the Berner Oberland, either in the valley (Lauterbrunnen), or in the mountain villages (Mürren and Gimmelwald on one side, Wengen on the other). I stayed in Mürren and would happily do so again (and unlike Chris, I don't live there and so have no bias).

Dear all,

Thank you some much for the wonderful replies, I have a clearer picture now :) :)

Well OK, compared to Murren and Gimmelwald, and even valley places like Lauterbrunnen and Gimmelwald, Interlaken doesn't fare well. But just imagine if it wasn't the gateway to such natural grandeur and wonderful alpine villages which eclipse the town - It would stand up pretty well as a destination by itself:
Caught between 2 sparkling lakes, connected by a turquoise river, with the Harder and Heimwehflue guarding the north and south, with many paragliders jumping off, only to land in the public park in the centre of town. Add to this the lovely ambience of the Hoheweg, with it's cafes, restaurants, casino, grand hotels of yesteryear (ignore the Metropole), mixed in with traditional Swiss architecture, and you've got a rather nice town

I've stayed there both times that I've been to Switzerland (last time in the brilliant Villa Sohnenhof), and have found it a great jumping off point for the Bernese Oberland and other parts of central Switzerland, as well as a very nice introduction to the area.. When I saw it for the first time I was entranced by the whole place, so much so that it became my favourite place on earth. Now I know better of course and I'm staying in Murren and Lauterbrunnen this year, but I still say that Interlaken doesn't deserve all the bad publicity it gets, and will always hold a special place in my heart.