Start standing with your legs comfortably apart, arms straight up, and roll your shoulders forward and dive downward into a stretch. Hang there as long as you need, letting your torso and legs relax and stretch. Lift your arms back up over your head and lift your torso up perpendicular to the ground. Hold, reaching out and stretching, and then drop back down. Bend your knees slightly before uncoiling to stand.
Next, reach all the way down, bending your knees, and touch the floor with the palm of your hand. Stretch here for an instant, and then push with your fingers and extend back up into a standing position. Do several of these while balancing on your toe box, and then do several of these while standing flat on your heels.
While in a standing position, widen your stance, and tuck your pelvis in, keeping your back straight. Lift your left toe up, pivoting on your left heel so your toe points out ot the left. Put your weight on your right toe box and lower yourself over your right foot, extending your left leg. After you go all the way down, push yourself up with your right leg until you're upright again, and pivot on your right foot, extending your right leg, until your weight moves over your left toe box. Completely extend your right leg, lowering yourself all the way down to the left. Push yourself up, rotate and repeat. Position your arms in the air for balance, and gently raise and lower yourself from one side to the other several times.
Then, bring your feet in to a normal width and stand on the edges of your feet. Keeping your back straight and your chest expanded, and holding an arc in your arms for balance, twist and lower, until you're sitting on the ground cross-legged. You may have to turn one foot to the instep to go all the way down. Touch the ground gently with your hands and raise to standing before twisting the other direction, gently lowering yourself to the ground in the same fashion, and then back up. The key is to keep correct posture while maintaining controlled, slow movemet.
In any of these exersizes, if you can't go all the way down, or need to grab on to something solid for balance and / or use your arms to lower or raise yourself, do what you can. Simply following the movements will add strength, and you will progress quickly in a matter of weeks. You don't want just stretchability, you want flexibility.