Reddit mentions of RoadPro RP9108 Bendable/Adjustable Neck Pillow with Memory Foam

Sitting on a chair is possible. Standing is possible. Depending on the practice, walking may be possible.

If you want to remain on a mat, there are various options, each with advantages and disadvantages:

• Sitting cross-legged, you can use support cushions under your butt, as well as under your knees/thighs (or on just one side) to relieve pressure on the ankle (though it could also increase the pressure). Since some configurations make your posture asymmetrical you may not want to do this over the long term, or you may develop an imbalance in your body, and more subtly in your mind. Some cushion sets are designed to support the thighs and knees.
  
  
• If you use a thick enough mat, you might kneel and hang your feet off the back edge of the mat, letting the ankles relax somewhat. This is considered bad form or even disrespectful in some temples; check with the practice leader.
  
  
• You also might try kneeling with a small roll of memory foam (like a cervical pillow) under the ankles, so the feet don't have to extend so flat. You might combine this with other support cushions (e.g., T-shape, below) and/or hanging the feet off the back edge of the mat.
  
  
• You can use a kneeling bench, which lifts the body weight off the ankles (though the tops of the feet are still extended on the mat, which could still be uncomfortable if the flexibility isn't there).
  
  
• You can kneel while resting your weight on a cushion placed horizontally or vertically between your legs in horse-riding posture. This can put too much pressure on the soft tissues between the sit-bones, so it can also be augmented with another cushion placed across the vertical one, in a T-shape.
  
  
• There is another lesser-known sitting posture called the Scholar's Pose or Shoelace Pose, which may or may not be of use. It requires some flexibility in the hips. Rather than spreading the thighs wide and crossing the shins, the thighs are brought to the front and crossed, and the lower legs fold back on either side. Most people require some cushion under the butt, if they can even achieve the posture. The feet are still pointed, which may put pressure on the ankle, but it's possible that the angle may work for you.
  
  
• You can change positions frequently
  
  Lying down is not ideal for most meditation, as it brings on dullness and sleepiness.
  
  I've written a great deal about posture in the past. You can check my posting history.