Uhm, it honestly doesn't matter with what form you platform jump, beast does not jump higher on surface than any other form. It does jump higher out of the water.
And I personally switch between mouse and mouse and keyboard and only keyboard quite some time, most of the time because I'm lazy, or other times when I want to aim while swimming towards another direction, which is only possible with WASD. And of course, all the hotkeys for form changing. I still don't understand how I got through 3/4th of the game with singing.