Switzerland (5 days 4 nights)

My mom, sister and I are planning to travel from Frankfurt to visit Switzerland for 5 days and 4 nights (11th Dec to 15th Dec).
We are interested in scenic tour, but nothing too adventurous because one of the traveler is 2nd trimester pregnant. Could you please advise on the itinerary that should be planned?
The plan that we are currently thinking is 1 day Mount Titlis, 1 day Mount Rigi and 1 day Lucerne city tour; but I could not think of anything to fit into the itinerary without having a tight schedule.

Please advise.
Thanks.

Welcome to MySwissAlps Ariel330!

You could simply base yourself in Lucerne for the 5 days. It's a wonderful city with interesting museums and plenty to do nearby. See the Lucerne page for all details. Zurich and Bern can be visited as a day trip, of you want. Both are about an hour away by train.

There are much more towns to look into, see here. Also you can take a look at this guide, which helps you planning.