We went the opposite direction in late June, 2011. We spent the night in Merano intending to drive Stelvio Pass, but the weather was so bad that we decided to take the low roads on that part of our Alps driving trip. From the pictures I've seen, Stelvio is the king of hairpin turns. Do a Google Images search and you will see what I mean.
We had a great time going south from Merano on SS238 until it met SS42. There we turned west and drove on SS42 until it met SS39. We continued on west to SS38 and turned left (west/south) on it. We followed our noses on into Varenna by going south on SP72. We did not take SS36 which goes through a lot of tunnels. You could reverse at least part of that.
Sondrio is the largest town along the way, but it took so little time that we just drove on, checked into our hotel in Varenna and had lunch there.
We were on secondary roads, but not with endless hairpin turns. We did not drive on SS38 through Bormio. It has lots of tunnels and twisty parts. We love the twisty parts, but after meeting some folks in Florence who had to go across Stelvio twice to see anything due to bad weather and us being snowed in at the top of the Grossglockner Hochalpenstrasse in Austria, we decided to skip Stelvio. Maybe next time.
We drove through some great farming and fruit orchard areas, and we did drive through Ponte di Legno. We found that drive just as much fun and as interesting as going over high passes. It may be harvest time when you go through, or that may be over.
I did a little Rome2rio search for Malè to Bolzano and came up with these results: https://www.rome2rio.com/s/Mal%C3%A8/Bolzano. The driving option is the most direct and takes SS42 all the way into town, but there will be some twisty parts. Zoom in on the map to see just how challenging those might be for you.
However you decide to go, check the weather. Some of the higher roads could be bad or even closed.
