My daughter is almost 4 months old now and has been co-sleeping with me pretty much since the beginning. I did buy a Arm's Reach Co-Sleeper bassinet with the intention of her sleeping in it pulled up to the bed, but she wasn't really "into" that whole thing. LOL. She slept in it a few times but was pretty adamant about sleeping next to me. I finally gave in so we could both get some rest.
We sleep in a queen size bed. Daddy moved to the guest room when I was about 8 months pregnant since neither of us were sleeping due to my tossing & turning from size & bladder issues, as well as me poking him to make him roll over & stop snoring. Since she was born, it's just kind of stuck that he sleeps in there most nights. Anyway, I sleep on one side of the bed in a normal position, and she sleeps on the other side with her head toward the center edge of the bed and her feet at my stomach. I was completely paranoid about her sleeping with me to begin with, too, with issues with blankets, pillows, etc. I pull the comforter off half the bed so it covers me and goes up to her waist, and I keep the pillows away from her. She's in a "sea" of open bed really, so I feel pretty secure about it. I often sleep with one hand on her tummy or holding her hand; if she wakes during the night, putting a hand on her tummy usually soothes her right back to sleep.
She's not rolling over yet (well, once -- she's working up to causing new issues quite soon), so that's something yet to deal with. I intend to put pillows around the bed, just in case. But she's really very centered on the bed, so she'll have to do a lot of rolling to make it off.
Her Daddy does sleep with us on occassion, and when he does, I sleep between the two of them with the bassinet pulled up to her side of the bed as a barrier. In this case she's just laying beside me with her head up toward the pillow. I think instinct keeps me from rolling over on her, though like another poster, I also had a cat who slept cuddled up to me, & we never had an issue of me rolling over on her either.
We do breastfeed, and I move to her position when she nurses so she can just fall back asleep without needing to be moved. I've fallen asleep myself a few times next to her without any issues, too. My lactation consultant says that we Mommies have that natural instinct that keeps us from rolling onto them in our sleep.
It's working well for us, though I'm sure it's going to be a tough fight later when I want her to sleep in her own bed.
You'll probably sleep very lightly at first worried about her, but that will pass. She'll be happy to be next to you, and soon you'll both sleep much better. Hope this helps!