I have a suggestion for a lunge variation. Keeping one foot planted, do a front lunge, then with the same leg do a back lunge. Keep moving the same leg from a front lunge to a back lunge. I did the first time with my right foot traveling and my left foot stationary. The next set I switched to my left foot traveling and my right foot stationary.

Todays WOD worked well for this since front lunges followed rear lunges. I simply did one leg for the first set then the other for the second. I could have just as easily done 15 seconds each side and switched.