windowsill herbs tends to grow out towards the light source (sun). You can pick the top leaves to contain the plant to a smaller size. You cam also pick them at lower levels so that these let the smaller leaves develop and grow. The result will give you a small plant but with many leaves growing for you to harvest.
I know I am so late suggest to you here for herb garden. Here are a few things to think about as you plan an vegetation such as soak the plant seeds in water for a few hours, set up the ground and bins for increasing the plant seeds in, Sow the natural herb plant seeds 1-3 times further than the size the seeds, Implant the vegetation by pinching off the reduced set of results in.