bath tubs ideas that won't break the back

Me and DH have been bathing the baby together in kitchen sink with blooming bath sponge.

Not very good on our backs specially mine for my height and weight, as tummy comes in between so I have to bend a lot.

She being growing and thinking our back condition, I started look for bath tubs but most of them had butt-rest, head-rest kind on bottom floor of tub which i heard is not very safe as baby keeps slipping.

So bought flat bottom with sling.

Since it was too high for kitchen top, we put it in normal big bath tub. Our bathroom is spacious but way bath tubs are made in US, it was extremely difficult kneeling down.

One person in big tub on side, hitting walls, one person outside bathtub to hold her...no one had good control on baby.

it was so unsafe,and so heavy on our backs that we did not bathe her well. Just soaked her and backs started hurting so bad, that took her out.

I had thought co-bathing but is so risky, so far sink bath is better and less back breaking for us.

So I wanted to know the ideas you guys bath and what bath tubs you use.

bath tubs ideas that won't break the back