I can think of two civs which would be great for this.
The first is Venice.
Venice gets double the normal amount of trade routes, which means you'll be getting roughly double the normal amount of gold than usual. Furthermore, they have the Merchant of Venice. In addition to being able to buy city-states, this unique great person gets a boost to trade missions - you get double the normal amount of influence and gold. This, of course, stacks with the Commerce social policy tree finisher. In addition, you'll only ever have one city that you'll need to put your full attention in to - the capitol. All other cities will be puppets - in which you will be able to buy buildings and units with gold and faith. This is the civ that was specifically made for your strategy.
However, doing a quasi-OCC is too limiting you for, there is an alternative.
The second is Portugal.
You get double the normal amount of gold from resource diversity from trade routes, which means you get quite a bit more gold than usual from your individual trade routes. Secondly, you get the Nau. Ship this ship to the other side of the world, find a city state, and sell your 'Exotic Goods'. Just one gets you quite a bit of gold/exp, now just imagine a whole fleet of these! In addition, the Feitoria will make it so that you never have to worry about happiness ever again. Plop one in every city state (Coastal tiles only) with a unique luxury resource, and your happiness will skyrocket. You won't have to spend gold or effort to ally city states for their luxuries, and because of all the luxuries you get for free, you'll be able to sell off every luxury in your own territory without your people going unhappy.
It depends on your play style. If you want more freedom over somewhat less gold, go with Portugal. If you want less freedom, but with boat loads of gold, go with Venice. If you're going for a diplo victory, go with Venice. With the Freedom ideology level 3 tenant that makes trade routes with city states give +4 influence per turn, you can easily hold a monopoly on them - It's like they pay you for gaining influence with them! If science is your priority, go with Portugal. They have an easier time getting techs, due to being able to have more cities. Couple that with the Freedom ideology level 3 tenant which allows for buying space ship parts with gold, and you have an easy path to the science victory.