We kept Lucy in the baby bath for a while after she should have 'grown out' of it. We used a support in that and then let her sit up in it. After that, we tried bathing with her in the big bath and then used a bath seat (she could sit unaided, but this was a bit of extra support and easier on our backs). The bath seat we got was the one that can turn but we never did turn it. I can't see why it's that dangerous unless you leave the room while the baby is in it and of course you'd NEVER do that while they're bathing. It was the circular type that doesn't clip or unclip, but you just lower the baby into it and stick their legs out of the front. It sticks on the bath with rubber feet on the bottom.

After she got too wriggly for the bath seat we bought a non-slip mat for the bath and let her do what she pleased (closely supervised). We only put water up to the point where it reaches her belly button while she's sitting.