Does anyone have a baby bath seat they can recommend? If so, when did you start using it? Do you have to wait until your baby can sit up on his/her own?

I'd love to bathe DD and DS together every night (it'd be so much easier!) but he's not a steady sitter yet. He sits for only a couple seconds before toppling over, so I obviously can't put him the big tub without any support, yet. There's so many options in bath seats, though, and I don't know where to begin!