A base to explore the mountains between Zurich and St. Moritz

Hello Switzerland,

I am looking for some recommendations for a nice place for my Dad and I to base ourselves for 2 nights or so to explore the Swiss countryside/landscape. I have been researching for hours with a combination of Google Maps/All Trails/Google but am getting a bit overwhelmed (and so much on Google is just crappy affiliate marketing stuff). Hoping someone can help narrow down my search with some locally-proven recommendations.

We are flying into Zurich and then getting the train into Italy from St. Moritz, so I am looking for somewhere in between those two locations that ideally meet most of the following criteria:

1. are in a scenic valley-type situation

2. a good base for day walks that aren't too crazy (my dad is a very physically active Australian farmer, but in his early 70s)

3. low-altitude enough for walks do be doable in late April

4. easily accessible by train/bus (although it seems basically everywhere in Switzerland is!)

Any guidance very much appreciated! Thank you!