Yes to everything Clare said about walking. Walking is great for cardio and powerwalking as well. And I absolutely love yoga, I just don't practice like I used to. If you still have P90X, Yoga X is in there, and it is one of my favorite yoga workouts. It is quite long, but amazing.
As far as the calorie burn for both of these, you probably won't burn as much as higher intensity cardio or heavy weight lifting, but you probably won't be as hungry either, which will allow you to eat fewer calories and thus compensate for the difference. Last year was my high intensity, ridiculously heavy weight lifting year, and not only I did not lose a pound, I ended up gaining 10 more on top of that. The thing is I was pushing myself way too hard almost every day and I was hungry all the time, and because I was hungry I was eating way too many calories. This year, I still do some hard workouts, but I also have days where I take my dog out for a walk, or I do some intermediate workouts. Every week I have a couple of days of high intensity stuff and other days I go for intermediate level workouts. I have some days to lift heavy and others I do a barre workout or something less intense than what I was used to doing. I have found I am not as hungry as last year, even though I had to make some changes on my diet due to medical issues, and I am starting to lose weight again.
This has been my experience and yours might or might not be the same, but I think everybody can benefit from a day or two of less intense workouts. I have read also that our stress hormones (cortisol, etc.) increase when we do high intensity exercise too often, which for some of us results in overeating.
The best thing about walking is that the only equipment you need is a good pair of shoes, if you do it during the day you can get the extra benefits of sunlight (vitamin D production, improved sleep, better mood, etc.). I also recommend Jessica Smith's YouTube channel which is free and has tons of intermediate workouts including stretching and yoga.
Good luck.
