Like, the people who were really big on Romulans seem to mostly be into the Rihannsu trilogy stuff, not anything post-TOS.
You can play as a faction of a remnant fleet of Romulans in STO (the closest you're going to get to a canon continuation of Trek). You have to pick to ally with either the Feddies or the Klingons (and can thus access their capitals, their ships, and questlines), but you still get your own capital city in the remnant fleet with some Romulan questlines and the ability to get Romulan ships (but IIRC now anybody can fly any ship now?). You get to fight Empress Sela and her empire.
Star Trek Online draws HEAVILY from the
Rihannsu series (there's four books in it, not three) and it manages to merge the two pretty well. Another series of books that help meld the Rihannsu style lore with the TNG style Romulans is the
Vulcan's Soul trilogy, which specifically set out to act as a bridge between the Rihannsu lore and Romulan lore from Nemesis.
They're probably my favorite faction of Star Trek as well (if the username, user icon, and signature didn't give it away) especially when using the lens of the Rihannsu series. I personally think that you can still see shades of the original "Honorable Roman" esq. portrayal of the Romulans in TNG era episodes, from "TNG: The Defector" to "Voy: Eye of a Needle" there's a more honorable streak to the Romulans that peeks through, and while you can argue it was treacherous, the Romulans were also the first power to truly recognize and understand the scope of the Dominion threat and sought to do something about it and protect the Alpha and Beta quadrants from them (DS9: "Visionary"), which is very telling seeing how while you can argue it was due to selfishness, the Romulans were arguably the power LEAST threatened by the Dominion as they had no territory near the Wormhole nor would they have born the brunt of the invasion.
If you want, one can even go so far as to "paint the villains white" with the Romulans when you consider how their actions always seem to be poking at the areas where the Federation is weakest, with plans and schemes that never actually seem to be fully capable threats to the Federation but are just strong enough to get the Federation to wake up and up their game. In TOS they were the ones that poked the Federation and got them to start paying more attention to military matters with an incursion across the Neutral Zone... just before the Klingons started some serious shit. Then in TNG they were the ones who started poking the Federation when the Borg began their scouting in the Beta Quadrant, while also upping the spy games with the Federation just as spy games were becoming more critical with the Dominion and ensuring that reactive elements in the Klingon Empire failed to take power ensuring a stronger Federation/Klingon alliance. As to a motive for them acting as a secret "mentor" to the Federation? Simple enough: making sure their original homeworld and kin are well protected. Heck, it was the Romulans who arguably created the Federation via the Earth-Romulan War, forcing the Vulcans into a proper alliance with others who would ensure their security.
Am I serious with this idea of the Romulans being, in effect, trickster mentors to the Federation? No, not really, but if you want to get creative with how you look at the Romulans they actually have a lot open with them.