This is the “ticks-all-boxes” lower-body exercise you never knew you needed. Not only will it strengthen your legs and bum, and generate better mobility (and flexibility) in the hips and ankles, it will also improve your stability. You do one leg at a time, which works each side of your body in turn, and helps with balance. Try not to wobble: staying still works your core.
a) Stand roughly 50cm in front of a chair and place your back foot on the chair (or sofa/coffee table).
b) As you would in a lunge, bend both knees, allowing your back knee to come towards the floor.
c) Do not allow your back to over-arch. Let your front hip flex, and lean forward, maintaining a long, neutral spine.
d) Return to the start position slowly, and repeat 15-20 times (you will need to reduce the number of repetitions if using weights for this).