It doesn't sound like you are changing the flavor of your campaign too much, so I would stick with whatever system you and your players are already familiar with.That's fair.
When I imagine cutting based D&D campaigns, they rely more on social and factional play but not to the degree that there aren't dungeons (or dragons for that matter). But the primary difference is that rather than exploring a whole world and adding breadth, the PCs are exploring a city and adding depth.
That is an interesting distinction. Why do you say that?Just use whatever system everyone is familiar with. You don't need special rules for cities. The wilderness, on the other hand, if you want "nature" to be a serious adversary, you need to be choosy about your rules.
It's pretty hard to kill anyone through starvation or exposure in the 5e ruleset for example, unless you introduce a lot of house rules. And other "heroic" RPGs are similar. Boring but essential stuff like food, shelter, and not being eaten by wolves whilst going to the toilet are glossed over by a great many RPGs. I don't really know of any that do it well, but I tend not to run that sort of game, so I haven't seriously looked.That is an interesting distinction. Why do you say that?
::googles::Cawood Publishing's Monsters of the City (highly recommended)

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.