When to move on from Sleep Bags & into a Big Bed?

DD is only just 6 months, so I know I am getting ahead of myself ... but have been wondering -

When did you stop using sleep bags and start on PJs and a bed with sheets/blankets?

Also, when should you look at transfering from a cot to bed?

Hi there, what I have found is that it will probably depend on the child. My first son was rolling from 5 months, so we started with the bag to keep him warm and also a sleep que.He is now 2 and we have only just taken it off. We moved him into a 'bed', which actually consists of a mattress on the floor (sounds bad but its an IKEA bunk, so it doesnt look like he's on the floor) at 14 months because we needed the cot back for the new baby, and initially surrounded him with pillows and toys and eventually invested in one of those mesh buffer thingy's. He probably doesn't need it anymore, but because he still moves around, we keep it there in case.
As for my 2nd son, he's only 9 months, but it appears to be a back sleeper as he isn't rolling, so I have no idea what to do with him, but he probably doesn't need a bag because he doesnt move all night, but, it still works as a sleep que, so I'll persist until he's old enough to cope without it - or maybe he'll always want it, who knows, lets just wait and see.