Exercise juice releases happy hormones in the brain, so get your butt moving
Just an FYI.
Here's something that you might try when you have only a few minutes to spare.
You might try some what we call
koshi-wari, butt split or butt squat, here.
Stand with your back against a smooth wall for support, but don't lean on it. Spread your feet apart wider than your shoulders--about two feet apart, making sure that your knee cap and toes are aligned, in other words, pointed the same direction. Keep your back upright and slowly lower your butt until it's knee high and hold the position for 30 seconds. Twist your shoulders to the left and right a few times if you can. You can place your hands on your thighs for this, to keep your balance. You don't have to do this multiple times at once. Just do it once for 30 secnds, 3 times a day. So, once in the morning, once around noon, once in the evening. If your knees/back hurts, hold the position only til just before they start aching.
Also, when you've gotten used to holding the position, you can start trying to do it without the wall.
This helps strengthen the inner pelvic muscles, which aren't easy to strengthen with weights and resistance exercises, and tighten up your belly from the inside, as well as help strengthen your knees.
This is actually one of the warm up exercises that our sumo wrestlers do, and is also one of the exercises recommended by our orthopedic surgeons for prevention and PT for back pains. Since those super heavy guys do it, it shouldn't be as much of a strain on your knees as regular squats are.