Personally, if I were going to write a romantic fantasy setting, I’d do an end-run around the cognitive dissonance between “progressive politics!” and “yay monarchy!” by supposing that the nation in question underwent a semi-peaceful transition to elected leaders and simply retained the old titles and their associated pomp, converting them into elected positions.
So you’d still have barons and counts (and the occasional marquis for flavour), and they’d still have fancy robes and palatial estates and whatnot, but it’d all be based on popular elections – something like the Canadian parliamentary system, say: five year terms, no term limits, and a single national election covering all titled positions at the end of each term, with each individual domain’s subjects voting for their own local ruler.
The elected nobles would then form a national legislative body, and nominate a king or queen from among their own number. The monarch would wield supreme executive power, but have no particular legislative authority (save for their single vote by virtue of their elected rank, of course).
Dukes/duchesses and princes/princesses, meanwhile, would have no relation to parentage, but would be the titles given to the heads of various government ministries appointed by the monarch. The rules for whether any given ministry has a prince/princess or a duke/duchess at its head would be arcane and deeply rooted in historical precedent; they’d all have fancy pseudo-Latin monikers, of course, but in plain English it’d be totally possible to be appointed as, say, the Prince of Public Sanitation. (It’s more prestigious than you’d think!)
A noble who retired or was voted out (or dismissed by the monarch, in the case of princesses et al.) would retain the generic title of Lord or Lady So-and-so; the title would carry no particular authority, but a certain amount of social cachet. The spouses of current and former elected nobles would likewise be styled Lord or Lady, but their children would not be.
And finally, in keeping with romantic fantasy’s recurring theme of magical contrivances rendering implausible forms of government feasible, the votes for each national election would be collected and tallied by an armada of incorruptible enchanted woodland creatures, thus ensuring that no fraud or overt manipulation can ever take place.
“You don’t vote for kings. Well, not directly.”
“Strange women lying in ponds distributing swords is no basis for a system of government. That’s just a ceremonial holdover from a less enlightened era.”
If your polling station has been well-behaved in past elections, your votes will be tallied by squirrels and songbirds.
If there’s a history of shenanigans, however, you get a moose.
The moose will not tolerate shenanigans.
The moose has ways of knowing if there are shenanigans.
And if you continue to be a dodgy polling station. You get Geese. And Swans.