Overheating or not warm enough has probably been one of the biggest worries for me since having DD, the best thing that relaxed me was buying a little temp gauge thing (the blue avent flower one that's for the bath too) so I always knew what the temp was in the room she was sleeping in. That would determine how I dressed her at night and I felt much more confident in my choices. Naturally I still kept an eye on her, but it helped me not worry too much. Now she's in her cot in her own room our monitor has a temp reading so I check that regularly.

We've just moved from swaddling to sleep bags and I also go by their guidelines with tog ratings and clothes, with the help of an oil heater on cold cold nights.