How old is your child? Is she able to sit up herself yet?
When we started immersing our young infant for a bath, we used the First Years Infant to Toddler Tub with sling (first photo, on the left). In the end, we didn't use the sling much since though it provided some support, I thought it got in the way of us cleaning the baby. The seat provided me some peace of mind in handling a slippery wet baby.
Once he outgrew this tub (around 6-7 months old), we opted for a basic tub and found exactly what we were looking for in the $7 IKEA Lattsam (second photo, on the right). It has rubber grips under the tub and in the tub to prevent slippage. We originally used it on our bathroom counter (and rigged up a tube to siphon away the water because the tub with water was too heavy to carry), and then just put it in the bathtub when our son started splashing too much. It's better than using the whole tub in my opinion even though we could do that now since it requires less water to fill it up to a comfortable depth, and I think it's cleaner and easier to keep clean. Since it is pretty large, I think he'll be able to use it until he is 2.5-3 years old.