Just wondering when everyone moved their LO's from the cot to the bed? Or converted the cot at all?

We are expecting a little brother or sister for DD when she will be 16 months and I'm wondering whether we need to buy another cot or whether we should be transitioning DD into a bed prior to then.

My heart and head say it's too early but she is my first baby so I really don't know and it's months away so it's so hard to say!

Any help would be appreciated - thank you