I FF from 12 weeks and have always co-slept with my DD, even the night she was born, in hospital. It's just the way she is, she wanted to be with her Mummy. She's now 8 months and goes down for the night in her cot and usually comes into our bed at 2am. We're gently phasing it out. I have to say, I didn't notice that I slept any deeper when I stopped BF and started on the formula, but that could just be me.
Co-sleeping was the best thing I could have done, I think. It was clear that she wouldn't have felt comfortable or safe sleeping on her own, so I did much of what stottie said above. I got more sleep, she felt more secure. It was win-win. She is sociable, happy and very trusting, and I'm sure that it's partly because we have always given reassurance and comfort when she needed it.
I used one pillow and wore a great top from Uniqlo - really soft thermal stuff, DD was in a sleeping bag on top of the duvet and I had a spare mattress poking out from under our bed just in case she rolled off (she never did, funnily enough).
If it feels like the right thing to do, do it. Just don't mention it to too many people IRL.