A chair can provide a very supportive seat for meditation. Put a mat over the chair if it is backless and slippery, then rest a bolster to lean the shoulders against. Put half or quarter blocks under the feet so that the student has 90 degree angles at the knee and ankle. Put a block between the feet and kick the heels out slightly. Put another block between the knees and belt the knees together so the muscles can release. Make sure the buckle of the strap is not on flesh. Feel the support of the props and the chair under you.
Sometimes a folding chair seems flimsy to sit in. Use two chairs with seats together and a mat over the seats. To give the student some back support, belt a bolster across the back of the chair. Support the legs and feet with blocks and a strap as above.
