Use postures which foster mindfulness. Pain and drowsiness hinder mindfulness. Zabutons are quite comfy in combination with the square cloth mats. The height chosen will depend on hip flexibility.
The above advice is fairly general and non-secular. From this beginning, questions do come up about “which foot on top?” or “how should the hands be arranged together?” Again, generally this won’t matter. However, what you will find is that certain postures impose certain stresses on the body. For example, meditating with hands on knees palms up is somewhat more effort than meditating with hands folded in lap. The EBTs are not so prescriptive even though schools of meditation often favor certain mudras (hand positions). Meditating mindfully brings about a certain sensitivity to body posture. You actually may find it interesting to explore different posture variations yourself before studying mudras. In this way, your study would be deeper since it would be informed by personal practice and experience.