Residence implies permanence. You intended to live there only until you were able to buy your new residence.
Doesn't this somewhat depend on the situation when there were two properties owned.
If the current home was let then I agree with you that the current occupation is temporary.
However, if the OP had two homes then they were both already residences. And the current residence automatically became 'the only or main residence' at the moment the other was sold. The fact that the op intends to sell it doesn't affect that determination.
If the OP made a cgt election previously then they could explicitly change their current home into their main residence (for CGT) the day before the previous home was sold by making another election.