Generally speaking it is beneficial to keep the spine and neck erect while meditating. For most people, it is helpful to have your hips above your knees and to tuck your sacrum forward. Sometimes this can be difficult, but with continued practice, posture, and equanimity (mental composure) sitting straight for longer periods gets easier and easier. For some it may be difficult to sit for longer periods on a cushion without back support, and that’s okay. Some prefer to use their cushion against a wall or the side of a bed. Depending on the duration of your sit and your body type, you may want to experiment with different postures – such as cross-legged sukhasana, kneeling, siddhasana, and burmese position.