Sitting position is important.
If you are sitting on the ground, you can comfortably put your feet crossed. You can sit in a Sahaja Asana, means in a way that is relaxed, not to put legs on top of another row or anything to make it more difficult.
If you are sitting on a chair or couch, that’s also fine. You have to put both the feet separately touching on the Mother Earth.
Doing the meditation while lying on the floor is not recommended.
Any stress on your body is not needed. You have to be comfortable to be straight, sitting straight, not putting your neck back or forward, just sitting straight, that’s all.