We are in the same situation and I was ready to put DS into a BBB (we had been abroad in August and he has to sleep in a BBB next to us, but didn't try to climb out once) ... however, DH and my Mum talked me out of transitioning him once we got home (my logic being the same as yours, and doing it while we have the time, and I have the energy!). I remember my nephew used to climb out of bed sooo many times until he finally went to sleep and wasn't wanting this to happen when LO2 is here! (my nephew had to go into BBB as he climbed out his cot!!!).
Anyway, we have "decided" to get another cot for LO2 and DS will transition from his cotbed to the bed part once he starts climbing out!! Hopefully as DS likes his bed he will not have a problem transitioning, and if he does, I have told DH that he is dealing with it, not me!!!