How did you make the switch from using a sleeping bag to using blankets in bed?

Moo is 19 months old & has been in bags since he was 6 months old. I've been looking ahead to going into a big boy bed & thought I'd try popping a small blankie in with him for his day sleep, just to get him used to it.

However the few times I have tried this he either thinks it's a big game & hides his panda under the blanket, or cries until I swap it for a bag again. As soon as he is back in his bag he falls asleep He is clearly used to the routine of his bags!

What were your experiences with swapping to a blanket? Everyone I know IRL uses blankets instead of bags so no help to me!