Hayley - I was unable to breastfeed my first baby and so I expressed full-time for her for 6 months - I did it and I'm proud but looking back I did very little other than express in those first few months and tbh my little girl watched a lot of baby einstein dvd's as it took so much time. I know she benefitted from breastmilk but looking back it was a pretty miserable 6 months.
Some things to think of:
you will need to express 6-8 times a day for months on end - including every couple of hours through the night - I had to set an alarm to express so that milk was ready for when baby woke up - the whole process was about an hour, every two hours. (don't forget after the expressing you have the washing up and steralising.
If you're worried about breastfeeding in public with big boobs, how about expressing in public? you need to do it every 2 hours so if you want to go out anywhere, even a friends house you will need to bring pump and stuff with you, (ice packs, containers, pump equipment), or never go out of course. you are worried about exposure I can guarantee you that people saw more of my boobs and my nipples when I was expressing than they If ever have when I breastfeed my other daughter.
Your baby will still feed like a breastfeeding baby - ie little and often, so whilst my formula feeding friends were giving their babies 6oz every 4 hours I was giving my little girl, an oz here, an oz there, sometimes an hour between feeds. She demand fed as if she was feeding directly from the breast.
I can see your reasons and I do understand the challenges of breastfeeding when you have large breasts (I am a 44G) but I think you that expressing is so so hard. Just be aware what you are letting yourself in for. If you do go ahead you need to buy yourself a hospital grade electric pump, I had an Ameda Lactaline which was really good.
Best wishes and I hope you are able to make an informed decision.