Try Kohler. They have a couple tubs that are 20" deep. I assume that 57" is wall to wall. Stud to stud is probably 60" (a stadard size). 39" wide is plenty assuming you are talking one person.
: I would like to replace a standard tub/shower tile enclosure (57"L X 39" W) with a nice soaking tub/shower. Can you let me know if this is even possble. My toilet is right beside the tub/shower so no room to expand there. I would love to be able to buy a soaking tub that will serve the purpose the current one does. Need nothing fancy just a stay at home mom who is tall who would love to spend time soaking. Please Help!