Bath time is a great opportunity to tech your baby multitude of skills.
I recommend bathing your baby in a toddler style tub from 2 moths of age. The feeling of water surrounding her body, the buoyancy, difference in movement can only be experienced in sufficient enough water which facilitates critical thinking, sensory experiances and gross motor development.
This would be my choice of tub.
I would not use the green plastic insert, I would instead use the Bloom pad to provide safety, softness and comfort for baby and the parents.
Similar tubs sold in IKEA.
Teaching your baby swimming promotes great gross motor skills and critical thinking skills.
If you have the opportunity to sign up for a baby swimming class I recommend doing so as early as 2 months of age!
You will most likely not use flotation devices in the class but the flotation devices are great to use when you swim with your baby on your own time.
Most of the flotation devices keep the baby in an upright position. It is good for safety but it will ruin your baby's natural instincts of swimming.
Here is a list of the flotation devices I recommend and use when I work with babies in the pool.