Why not pray the full 15 decades every day?
For the past few days I prayed 45 decades ( 3 rosaries) daily, and the graces I obtained from it have been a great help to me, in practical terms as well as spiritual.
Or for extreme penance, try saying the rosary with arms outstretched and feel some of what Christ suffered for us on the cross for hours. It is something I just tried today and it is an eye opener.
Many agonies were those of Christ our Lord.