Hello Judy and welcome to the forum!
I am picturing the large step in two different ways; one is a long horizontal step, the other is a long vertical step (or combination of the two). If it is a long horizontal step, some stepping stones from the big box store will suffice. If it is a vertical step, you could go to a mobile home dealer and get a pre-formed concrete step (some have a fiberglass step which is lighter and easier to handle). Let us know how you come out with it.