Zurich, St Moritz, Portofino, Nice

That itinerary will call for a substantial amount of travel time--more than I would want, especially for a honeymoon.

Same reaction: your plan involves a lot of travel.
The Riviera, Italian or French, can be very quiet in February, and is not at its best - March or April would be better.
I would focus on winter activites in Switzerland, if you can afford it. If you still want a bit of "italian flair", instead of Portofino, you could spend 2 days in lake Como before flying out of Milan. Lake Como is also not at its best in Feb, but it is close to St Moritz, so at least you do not waste too much time getting there.

I would stay in Luzern rather than in Zürich.

And you could easily spend 5 days in the St Moritz area. Unless you can afford the best hotels there, which have a lot of "old world charm" (e.g. Suvretta House or Badrutt Palace Hotel), I find St Moritz itself to be a bit charmless, despite the beautiful location.
Instead, in winter I would recommend:
- Pontresina.
- Sils in Engadin, small place, at the foot of the Corvatsch and between 2 frozen lakes (well, usually frozen)
- Celerina, next to St. Moritz, with less concrete. In summer, I would have said Samedan instead, but Celerina is more convenient for winter activities
- A bit further afield, Bergün, a very cute village in the Albula valley with an iconic sledding trail.

EDIT: I forgot to add, and this is important: check that your insurance policy covers sledding/tobogganing. The risk of injury is high. Specialized winter sports insurance should cover it, but double-check. And use a ski helmet.

To provide additional "food for thought", in late January 2020, to celebrate a 'milestone' birthday with my partner, we spent a sledding/tobogganing-focused week in the Graubünden region of Switzerland and it was amazing.

We first spent 4 nights in Klosters, at hotel Piz Buin (with amazing sleek facilities including an incredible spa, and spacious rooms). Klosters is a charming ski resort linked to the more famous facilities at Davos, and there are plenty of winter hikes (especially above Monbiel) and tobogganing trails (Rinerhorn for thrills) in the area.

Then we spent 3 nights above Pontresina, at the amazing hotel Muottas Muragl perched at 2,500 metres above sea level, surrounded with winter hiking trails and with only one non-mechanical way down: the toboggan trail 😅. Downside: it takes a while to go anywhere else (although it's not as bad as it sounds), so not great for more than 3 nights I'd say unless you want to relax.
Delicious food there, by the way.

Both locations would be very "honeymoon friendly" I'd say.

St. Moritz to Portofino: 5 hours driving, 10-11 on trains or buses. Renting a car one-way is cost prohibitive and a 10-11 hour transit day is costly in time. Skip Italy and the south of France and enjoy the winter wonderland that is CH.

Balso has some great ideas! Makes me want to go back in winter. I also agree you should skip Zurich and go immediately to Luzern.

Counting in nights, spend 3 in Luzern, 4 or 5 in St. Moritz or Pontresina (more charming), then perhaps the remainder in Lausanne, taking the Glacier Express across the country from Pontresina/St. Moritz to Montreux and on (an hour) to Lausanne. Fly out of Geneva which is one hour by train from Lausanne.

Hi All - thank you so much for the advice! We are now convinced to do all winter in Switzerland! A few more questions, Thoughts on St. Mortiz to Zermatt on the glacier express? Any ski resorts we shouldn't miss? We are good skiiers, but not trying to do the hardest mountains, just the best ones!

Thanks again for all your help!

I absolutely love skiing in St. Moritz. In my opinion it’s one of the best ski resort. I’d also recommend going up to mount Corvatsch for the incredible views. It’s almost as high as the Jungfrau Joch. By the way since you want to go skiing it’s best to stay in Celerina, St. Moritz or St. Moritz Bad (which is even less charming than St. Moritz but maybe cheaper). From Samedan or Pontresina you’d have to take a bus or train to get to the skiing area.

Regarding Lucerne, its famous carnival (Fasnacht) will begin on 16 February. The big parades will be on 16 and 20 February 2023, in case you’re interested. Lucerne will be crowded though between 16 and 22 February.

If you take the train from St Moritz to Zermatt, you could perhaps stop in Bettmeralp for a couple of days. The area, marketed as the Aletsch Arena in winter, is basically a car-free plateau with mostly mellow ski slopes and incredible views of the Aletsch glacier and surrounding mountains. In full transparency, I have yet to go there, but it is high on my list and I thoroughly researched it.

Skiing in Zermatt is also excellent (tried and tested 👍) and it is cheaper to visit the various viewpoints with a 1-day ski pass than with pedestrian ride tickets. Plus, with skis, you can easily go to Rothorn, Gornergrat and Klein Matterhorn in the same day, or at least the latter two.

The Glacier Express also passes by Andermatt, which is most famous for off-piste skiing (guide & avalanche gear needed) off the Gemsstock. The newly-built piste skiing area between there and Sedrun doesn't look too great in comparison (short runs).