Half and Full Lotus Pose are great poses for seated meditations, but only if it is comfortable for you. Padmasana is not ideal for everyone, as there are many factors involved in order to find comfort in the pose. Flexibility in the hip, knee and ankle joints is a huge factor. Body structure is another, because if you are very muscular, you may not be able to tighten up the knees enough in order to fold the ankles on the thighs. Please practice with caution and care.
You do not have to practice Lotus Pose in order to have a great yoga or meditation practice! Other poses to try are: Siddhasana and Sukhasana.
The most important thing is to find your comfort in every yoga pose. Watch the lovely Mariko demonstrate how to get into this classic meditation pose.