I use the angel care soft touch bath seat. I just hold him and wash his bits first so they’re all clean then sit him in the seat and wash everywhere else and let him play
Just get an anti slip bath mat. Don’t get a seat and let her just move around
What I did with my other little when they could sit was to put a bath mat in so they can’t slide and of course shallow water as I found the sit up chairs a bit of a hassle