What is an ideal bath tub depth for use as a soaker and a walk in shower.?

we are putting in a new bathroom and want to buy a bath tub that will primarily be used as a shower stall.. meaning we have to step over the edge to get into it ? currently the one in our house is about 17 , but most these days are 20 ” is this going to be uncomfortabele/ dangerous ? can we lower the tub into the sub floor

Even a small step up and in can be dangerous because of the possability of slipping.. I ve tile many a tub w/ only a 14/15 in step up and over..I was led to believe from one of my builders that was the new norm for saftey.. Keep checking around and you ll find the lower style tub GL