Couches are regularly very low. For a taller individual, their knees can wind up being higher than their hips when sitting. This tips the pelvis in reverse and squeezes the lower back.
Choices are to sit on a pad to raise the tallness, to rests or to have a something a similar stature as the couch seat before the legs. Here you can have your legs extended out, maybe with a pad under your knees to keep the knees marginally bowed.
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