I breastfed for 6 weeks then decided to switch to a bit of both (did this for a further two weeks) then was exclusivley formula.
I began by cutting out the night feedings after I pumped before bed (I had about two-three bad mornings of waking up saturated in milk and couldn't lay on them by the time it was the early hours because it was uncomfortable) ,but I would pump when I got out of bed to ease discomfort and prevent mastitsis. It was maybe horrible for 2 days and by the 3rd getting a lot better.
My body soon figured I didn't need the production at night and drastically reduced. I wore a good tight bra, this seemed to help. I just ended up missing more and more pumping sessions in the day (often unintentional) and this really helped. For instance I had a few days out where it wasn't convienient to do so, and it went from there. To be dried up completely only took about 2 weeks if that..must admit, I feel amazing now. But do pump if it's getting painful. Be gradual. I thought it would take longer than it actually did.