It's unknown what type of ships the Romulan flew in the years between their acquisition of the Klingon D7s in the Mid 23rd Century and the appearance of the D'Deridex of the Mid 24th Century. So these are two possibilities I came up with.
The Belavis-class Romulan Warbird was the first true Romulan Warbird in over 30 years, which improved on the Klingon D7's design and introduced capabilties that were en par with the new Federation Excelsior class and the K'T'inga-class starships. But due to lower manuverability and high energy costs, this ship was quickly phased out in favor the Verterax-class.
The Verterax-class was believed to be the first Romulan Warship to be equipped with the Quantum Singularity Drive, that became the trademark of Romulan ships of the late 24th and early 25th Century. While designed to combat the new Federation Ambassador class, and was proven to have a slower turning rate against it. It's believed four of these ships were used at the attack on Narendra III and defeated the Enterprise-C. Though Romulan commanders viewed that the design could have more room for improvement and invested in a new starship design that later became the D'Deridex. Currently, a few squadrons of Veterax-class ships were believed to be still in service, and several more reported returning to active duty after the destruction of Romulus.