I do not have twins, but breastfed both of our children. Personally, I did not like the Boppy because it didn't stay close around my middle and wasn't at all helpful for proper positioning.
I would recommend My Brest Friend (that is how it is spelled) because it can be tightened around you with a strong velcro strap, and it is flatter and much firmer than the Boppy. The only bad thing was the velcro strap is noisy to open when removing it, so if the baby falls asleep nursing, slide out of it or keep it on until you lay them down.
You can buy it online or at Babies R Us. According to their website, MyBrestFriend.com, they will have a twin version available this Spring.
Look into la lache league, see if your hospital or any area hospital has a breastfeeding support group but definately line up a couple friends or family members that can be there for you for breastfeeding questions and pep-talks.
Best Wishes to you and your twins!