I have a 1930s cast iron alcove tub which at the moment with tile on 3 sides measures 57.5” by 29” . It’s outside height is 17” which we find perfect for use as a tub or a shower. So my question is what size tub do I look for that would give me that height as I assume that it is a standard 30 by 60 and I will have to order before demo begins. I see tubs described as 18” high. Is it likely that would that end up around 17” high to step over? Thanks.