Bridges are an amazing exercise – great to use for a dynamic warm up.
Obviously, a short bridge and straight bridge are less challenging. A natural progression would be
Short Bridge > Straight Bridge > Full Bridge
If your goal is looking for exercises that are “good for your back” – I’d add other planes and sources of instability before attempting a full bridge.
Currently you’re only creating sagittal plane instability. For maximum lower back stability, I would add anti-rotational variations in the
- Transverse plane (Bridge with one leg out)
- Also sagittal plane instability (a common variation I like to do is put a TheraBand around a patients waist and pull outward parallel to the floor (varying the force throughout) or side planks is an simple version of this)
You can also alter the stability of the surface you’re on (straight leg bridge with your feet on a stability ball)… there are tons of possibilities and effective progression patterns.
Essentially for lower back stability you want to be targeting the innercore (not your global back musculature such as your lats for example). Targeting the TrA (Transverse Abdominus) and deep lower back musculature (Multifidi) and your pelvic floor muscles (if you're a fan of Kegel Exercises I'm not) is the way to go.