With the name of Herbert, you should fit right in. As you know, Herbert L. Clarke was the first person to teach soft playing. As you are trying to get your lips in shape you might try his first exercise in the Clarke Technical Studies, where he recommends playing pianissimo and decreasing the volume until the sound is barely audible. This helps the player focus the lip aperture to the point at which there is just a thread of air coming through. If you can keep the sound steady and smooth, you're on your way to longer and louder sounds that will be much more focused.