We used a co-sleeper until she was big enough to roll over (back to front and front to back) and I knew she was aware enough to move away from me when she was too warm ... About 5 months. Same as prior posters when it comes to sheets, etc. She is dressed so that she doesn't need covers, and I keep them down around my waist.
I burp her if she rolls around after nursing. If she drifts right back to sleep, I let it go.
FT mama to DD (April 2011), PT-WAH lawyer
Married to my best friend (October 2009)
Lovin' that BFing