My answer is “tons and tons”. If they have written something down in the form of letters or an autobiography, it can be construed as advice for lay people. For example, I was just reading today from a book that consists of many short quotations on the spiritual life from the letters and autobiography of St Therese of the Child Jesus. It is not an explicit “advice for lay people” work written by the saint, but indirectly, it is.
Any doctor of the Church would be good to consider reading. There are 35 of them. Francis de Sales is just one of them.