Hi E.,
I tried a method in a book called On Becoming Babywise by Gary Ezzo. It is based on a feed, wake, sleep pattern that helps babies situate their sleep and eventually gets them to sleep through the night. It also helps you to regulate your milk supply. The method is meant to be started when your baby is a newborn, but the book states you can start it at anytime. My daughter started sleeping through the night at 9 weeks! I sware by this method and tell anyone who will listen about it! Aside from the occasional week or two of her waking up in the middle of the night for growth spurts or teething, we have had really good results. I am so glad someone recommended this book to me. It involves setting her up on a routine during the day, so you may have to change what you are currently doing, but the end result is soooo worth it! It can't hurt to try it.
I also read that some child development experts recommend putting your little one down by 7:30pm. For some unknown reason, babies put down at that time sleep better. When my daughter had her first "off" week, I started reading up. I used to put her down at 8. I pushed the time back a 1/2 hour and we were amazed! Sleeping through the night again!
I am fan of doing whatever works for the person and their family, but at this stage of the game, I wouldn't advise co-sleeping. It will just be a sleep "crutch" rather then a way of getting her to sleep through the night on her own.
Good luck with whatever you try!