That route will not go through the town of Sonoma. It is a straightforward trip taking you to Hwy 101 with no scenery except some vineyards before Hwy 37.
If you have some time you can go over to the coast, visiting Armstrong Grove Redwoods State Park on the way, and then back to Hwy 101 at Petaluma or continue on Hwy 1 to San Francisco.
Take 29 south as before, then 121/12, but watch for the turnoff to the town of Sonoma, which is about 25 miles. After you have explored the Sonoma Plaza and anything else you want, go north on 12 to Santa Rosa (22 miles). Cross Hwy 101, staying on Hwy 12 to Sebastopol (7 miles). This is a cute town. Then north on Hwy 116 to Guerneville where you will find Armstrong Grove. (15 miles). If you want to visit the park (it is a good one, better than Muir Woods) watch for signs or ask for directions. The Safeway in town has a good deli if you want to pick up picnic supplies, or browse the main street for a more authentic one.
From there stay on Hwy 116 for about 11 miles to where Hwy 1 comes in. You will turn left and cross the Russian River, It is 10 miles on the coast to Bodega Bay, which is a small fishing village. Alfred Hitchcock filmed some ot "The Birds" here. Lucas Wharf has a nice restaurant, a gift shop and a fish market.
Now you have a choice.
1) You can continue on down Hwy 1, which goes inland at this point until Tomales Bay, which it skirts, and past Point Reyes National Seashore. This is over 60,000 acres and is hard to visit in just a short time, but you could drive in to the Visitor Center at Bear Valley and get some information for another visit. Or not. It is 34 miles from Bodega Bay to Point Reyes Station. From here, it is 28 miles, with some high cliff driving until Hwy 1 joins Hwy 101 at Marin City.
2) If this is too ambitious, after Bodega Bay do not make the right turn to stay on Hwy 1. This is about 5 miles from BB. Instead stay on course and go through some rolling hills to Petaluma and Hwy 101 (26 miles). Petaluma has a cute downtown with some antique stores. You are not about half an hour from the Golden Gate Bridge.
I think you would really enjoy this trip.