You will pass right through several small towns on Lago di Como on your way between Tirano and Verona (you have to get to Milan to catch the train to Verona). You might as well make your Como stop then, as on the way back to Zurich it would mean a detour, unless you wish to stay in the larger and less appealing city of Como at the south end of the lake. through August you will have a bus link between Tirano and Colico before you reach the lakeside towns, so do not be surprised by that. Use Trenitalia.com to view the routes and schedules. town names must be spelled in Italian.
We have read in this forum that lodging in Varenna, the most popular small town, is scarce at this point. Also try Bellano, another lakeside town on the train line just north of Varenna. Or look at Menaggio, directly across the lake from Varenna and connected by a short ferry ride. You can get to Milan for onward travel to Verona by bus from Menaggio to Lugano (a lakeside town in Switzerland) and then a short train ride to Milano Centrale.
It might help to look at a map of the Swiss and northern Italy train lines. Varenna is not on the map but Menaggio is. Milan is just off the map at the bottom.
https://www.travelswitzerland.com/en/download/swiss-travel-system-map-en-2023/?wpdmdl=14294&masterkey=63a023c8da36c
From Verona you might consider heading to Malcescine on Lago di Garda for your beach time, instead of all the way down to the Italian Riviera. Most hotels there can arrange a shuttle to [pick you up at the Verona train station, and return you there after your stay. Or you could ride a ferry down the lake to Desenzano and pick up the train there.
https://www.visitmalcesine.com/en
To return to Switzerland at any point you have to go through Milan again. Unless you want to take the Bernina Express in reverse. but the best option for August travel is the train from Lugano or Locarno in Switzerland over the Gotthard Pass. This is marked as a scenic route on the map I gave you.
I will make one lodging suggestion and that is for Verona. The town is busy in summer due to the opera in the Roman amphitheater, but I found reasonable prices and family rooms for our visit last September at Pepita Lodge, just outside the city walls and a 10-minute walk from the train station.
http://www.pepitalodge.it/en/