My starting equation was: great baby 9 months (80CM / 10KG), no bath in my house, Bath pokey on foot. It gave: painful bath where baby can not move and has no place for his toys and parent to backache.
Solution: Shower Seat Opla! My little well be "wobbly" in a sitting position, it is held by the walls and sloping seat. FINALLY he laughs in his bath, and I just take this moment, without retaining its weight with my arms :-)