Thoracic Bridge Series- No Bars & Need Progression

Are stall bars necessary for this series and can any stall bar work be scaled?

using either a flat wall or raised box for elevated bridge stuff is possible. ive used the boxes they use for jumping at the crossfit gym for teaching bridge progressions and having something with an adjustable height is nice but you can also make due with some steps, couch, bench, chair and if you can keep your feet stable, on a wall.

got anything that fits that criteria that you can safely use?