Convert to the Citi Rewards+ card. It's a no-annual-fee card that earns TYP points, and thus preserves TYP points when you convert either Prestige or Premier to it. You won't get the ability to transfer to most airlines until you get another AF card (ie, either Prestige or Premier), but you will keep your TYP points.
But "new" cards in the past 2 years don't matter any more. The current terms on a Premier card are:
"
Bonus ThankYou® Points are not available if you received a new cardmember bonus for Citi Rewards+℠, Citi ThankYou® Preferred, Citi ThankYou® Premier/Citi Premier℠ or Citi Prestige®, or if you have closed any of these accounts, in the past 24 months.
"
So how long ago did you get the
signup bonus points for your Prestige card? That's what matters now (as long as you don't close the Prestige, or convert it to a non-TYP card that Citi may treat like a closure)!
So if you got that signup bonus well more than 2 years ago (ie, if your annual fee is due now, and you haven't had a new CIti TYP card in "over 2 years", that implies you must had the Prestige at least 3 years, right?), then you could apply for the Premier right now, before you close the Prestige.