Co-sleeping safety rules:

Babies should NOT sleep in your bed if:
you are very heavy sleepers
you cover baby with a duvet (?doona) or baby is near pillows
you smoke, are drunk, or take illegal ("recreational") drugs
you are excessivly tired
baby should sleep at the edge of the bed, not between parents for risk of overheating

Having said that, DS snuggles in the middle of us, under the duvet, up with a pillow... although at first DH slept in another room so DS could sleep with me safely (his choice - he didn't want to be woken up, although we have co-slept three in a bed on occasion, particularly at my Mum's house). I did at first have DS under a sheet on top of my duvet but my arms got too cold so we snuggled up together under a very light duvet. DS was always in my arms so he couldn't move below the duvet or climb up to the pillows. He wasn't that wriggly either in the first year, which helped my decision.

Practicalities. Well, I started co-sleeping because I'd be falling asleep while feeding DS at night so figured I may as well do it as safely as possible. Took him a while to latch on lying down, but it was worth it. DS always started in a cot next to my bed and came into bed when he woke up. I think if he can raise his head with a blanket on it then he'll be fine with a duvet and pillow, especially as his head's above the duvet and I'm holding him next to me.

DS now likes to sleep alone unless he's teething. When he's teething, he likes my bed, but to lie right in the middle of it, horizontally, and kick. DH gets kicked so hard he's left the bed within ten minutes, but I just have to live with it if I want sleep. DS prefers to sleep alone mostly and if anything is wrong other than teething he screams blue murder if I try co-sleeping.