If you've ever watched water polo, it may be surprising to see the athletes swim with their heads above water. The function for them is of course to be able to see the ball and other players easily, but it can be helpful for triathletes, too, when working on holding a high cadence. With your head above water, your lower body wants to sync, and it become virtually impossible to glide at the front of each stroke.
Use the water polo style as a drill at the start of your workouts. With the chin on the waterline, swim a 25 or 50 peeking forward at your arms as they enter the water for each stroke. In addition to the higher cadence you'll naturally have to carry, you'll also be able to see the hand entry and extension of each stroke—win-win! Follow each water polo drill with the same distance of a moderate effort freestyle. It will likely feel much easier and smoother to hold this clip. It can be helpful to use the tempo trainer during these sets, too, further integrating the new, higher tempo.
Consistency is key here, so commit to slowly working your stroke rate up to your sweet spot, while always staying aware of how you're breathing. Keep your breath relaxed, as always, being sure you're not trying to work with too much air in a shorter period of time.