I've had Izzy in her 2.5 tog bag for the last 4 nights or so with a long sleeve pyjama top on underneath but no legs. Last week whenever we had that first cool night she had legs too.

I basically dress Iz according to how we are feeling at night (or at least DH at the moment until my pregnancy heater disappears!). We have a latex bed which is very warm and while DH sleeps in jocks only, he's got the winter doona pulled up to his ears by early morning, not to mention his hot water bottle wife.

I would be inclined to dress Felix for the early morning cool, given that he's going to wake up if he gets cold and wake his mummy!! Just make sure he's not too hot when you put him to bed at night. Depends on Felix's room obviously, but we leave Izzy's sliding door and two windows open when she goes to bed, but then close them to stop the breeze when we go to bed.

And having waffled all that, just give the warmer grobag a go and see what happens!