Question to ask yourself:
How would you rest your body if you didn't have furniture?
Here are some examples of possible sitting positions:
How would you rest your body if you didn't have furniture?
Here are some examples of possible sitting positions:

One of the main things to assess is whether you are able to sit with a neutral, untucked pelvis, with the public symphysis on the same line as your ASIS.
To help your transition to any of the above sitting positions, use stools, floor cushions, stacks of blankets or a half-dome to help you untuck your pelvis and sit on your sitting bones.
You can also start from the chair and bring the floor up, to start introducing new angles of flexion (investing in a squatty potty or having your feet up on a stool when sitting at your desk or dinner table)
Focusing your efforts on the mobility of your ankles, knees, hips and pelvis will be very helpful too! Focus on progress. Making one step towards sitting on the floor is progress. Take photos and compare in six months to a year and again another year later.

If the floor is too low yet, simply vary your positions on your couch or chair.
Choose a slightly lower seat.
Choose a slightly lower seat.
