I strongly recommend taking California 25. Heading south, you pick it up off of 101 near Hollister. Right where 25 branches off of 101 is "The Garlic Shoppe", a great place to stop for all things garlic or cooking in general. Head south on 25 for about 60-65 miles where you'll intersect with 198, then west on 198 for 10-15 miles or so and you're back on 101. Heading north, (which I now realize you likely are), do the opposite - pick it up at 198. Also, if you have a little time, 25 runs past the eastern entrance to the Pinnacles National Monument. A worthwhile detour if you like nature type stuff.
A cool place to stay for the evening is Sycamore Mineral Springs Resort in Avila Beach, just a little south of San Luis Obispo. Even if you don't stay there, you can check out the hot springs/tubs. They have a hill you walk up with very private, naturally fed, hot tubs along side paths on the hill. Outdoors, romantic, relaxing.
Bill