If your legs swell badly, it means lymphatic circulation isn't functioning properly.

I also often experience swelling in my legs and a heavy feeling in my legs.

The main cause is said to be the poor circulation of the lymph nodes, and among yoga poses, the best posture to help this circulation is the Cobra pose.

It is said to evenly stimulate the posterior lower body from the hips to the soles of the feet, helping with stretching, flexibility, and blood circulation, thereby assisting in reducing leg swelling.

I do Downward Dog every morning, and I think I should try the Dolphin Pose as well.

Dolphin Pose

Dolphin pose, which looks similar to downward dog; a yoga pose. In yoga terminology, it combines "shishula," meaning dolphin, and "asana," meaning pose, and is called "shishulaasana," or dolphin pose in English. Unlike downward dog, which supports the floor with palms with elbows extended, dolphin pose involves bending the elbows to support the floor with the forearms. Since the center of gravity tends to shift downward in the upper body, it strengthens the muscles that push the upper body away from the floor, as well as the shoulder and scapular stabilization muscles. Like downward dog, it also involves pressing the tailbone toward the ceiling and straightening the knees, which is good for stretching the lower body and improving blood circulation.

Source leia_illust