You could try static lunges, which is just holding that lunged out position with your feet, lowering into the lunge as far as you're comfortable, and coming back up. You could try the normal lunge without weights added, then if that doesn't hurt, work your way back up to holding added weight. Another good option is step-ups...similar training effect, but I found it easier on the knees. Just use a sturdy step or box or bench of whatever height you are comfortable with, step up, touch the trailing foot on the box or "stand" on the box, your choice, then lower back down...do half your reps with one leg remaining on the box through those reps, then switch legs (or however you want to break them up). Walking lunges may be another option, if you have the space, and it's just like it sounds: take a big lunge step, lower as far as you are comfortable, then the other legs steps forward into a lunge, so you're alternating right/left/right/left. I find those more comfortable than normal "step forward, step back" type lunges. Just experiment, until you find something that doesn't hurt that knee. I did step-ups for a long time, but after some of the weight came off, I found I could do static or walking lunges without pissing off my knees.
PS- your idea of lunging to a step would be a great alternate, I just wanted to give you some other options and ideas, too. Also, if the videos have you doing lunges every single day, that may be part of the problem. You may want to alternate days with another activity or video that doesn't include lunges, or just sub out the lunges for something else, like do deadlifts or squats or abs in place of the lunges, just to keep moving during that time slot. You could also put into something like jumping rope or peddling a stationary bike, box jumps, walk in place...get creative, so you're not burning your legs in the same way every day.