Knee-Friendly Lunge Variation

In general, when it comes to cranky knees and lunge variations, a stepback lunge is going to feel better than a walking lunge or forward lunge, as stepback lunges are much less decelerative in nature, thus there won't be as much eccentric stress on the knee joint.

However, once you're ready to progress to slightly more advanced variations, try a forward lunge to step as your first progression:

The step/box makes it so that you don't have to decelerate as much of your bodyweight compared to doing the forward lunge in its standard fashion, where you simply lunge forward until your foot contacts the ground in front of you. You can start with a high(er) box height in the beginning, and slowly lower it as long as things feel good.

Sometimes, this variation feels better on the knees even more than a stepback lunge!

I'll also note that no lunge variation is knee-friendly when it's executed with terrible form. You'll see a lot of individuals performing lunges and split squats with a pronounced anterior weight bearing posture - they'll shift their weight toward the toes and allow the knee to track far forward - so often times helping folks to learn to use their posterior chain and how to properly distribute their body weight during lunges is a great start in and of itself.