Hey there, I am also exclusively expressing and I'm nearly at 13 weeks in, doing it for same reasons as you I suspect . Being nosey, how much do you make a day, how many pumping sessions and how long at the pump each time? For me it's about a litre, six sessions, 15 mins each time.
If you would sort of like to carry on, my response would be:
Yes, it's bloody hard but I express in nap times and more in the evening and when DH is home. I think over time by pumping different amounts at different times you can train your body to produce more milk say, in the evening when the kids are in bed. This is what I have managed to do.
Does she sleep through? Mine doesn't, so I feed, resettle and sneak on to the pump. He naps three times a day so I pump then too, quickly. You can leave it up to six hours between pumps if you have to, you may only need to do five sessions a day, or less depending on your answers to the above.
CBeebies will buy you 20 mins of time (shoot me for saying it....!)
I have a list of dates and a calendar I tick off - ie get to Christmas, get to New Year, get to 4 months, get to 4.5 months and all of this is really motivating and pushing me forward. Not long till weaning and the pumping sessions can start to come down, or stop.
BUT, if you really do want to stop, my answer would be:
Stop. God knows you (we) have done enough!! Just pump a bit less each time and leave it a bit longer between sessions and, gradually, your supply will come down. Maybe drink a bit less water.
I would get some cartons of formula ready made and mix a little bit with your breast milk (knowing that you will have to bin the feed after two hours) just to get DD gradually used to the taste.
Hope this helps a bit.