Using ferrofluids to make magnetic gravity possible is literally the worst idea ever
First of all, ferrofluid simply doesn't behave like a fluid that sticks to iron. Have you seen what ferrofluid does in the presence of a magnetic field. It forms spike-like structure like the one in the image below
Unless you are a chad-transhumanist species that has adapted to all kinds of inhospitabilities in space, then, I wouldn't like to have my arteries bulging out in spikes whenever "gravity" is turned on.
Even if you forgot blood and went ahead with putting ferrofluids in the flesh, organs and all other parts of the body, you run into the serious problem: Magnetism increases dramatically as you get closer to the magnetic source.
Gravity decreases gradually the further you go away from the mass that is generating gravity. Gravity decreases with the inverse square of distance, or that the gravitational force is proportional to $1/r^2$, whereas magnetism on the other hand decrease with the inverse cube of distance, or that it is proportional to $1/r^3$
Do this activity: Take a magnet, and gradually bring a iron nail closer to it slowly. At a certain point, you suddenly feel a tug on the nail. The magnet is pulling much harder on the closer side of the nail, than on the further side.
Gravity is basically the only force that doesn't dramatically increase the closer you get to the source. That's the opposite with magnetism. The closer you get to it, it increases dramatically. If you had ferrofluids in your body, the "gravity" would pull on the side of the body closer to the magnet, i.e. the foot, more than it does on the further side of the body, i.e. the head. This can tear you apart.
Furthermore, ferrofluids are nothing more than a bunch of iron particles being dissolved in a solvent, most commonly vegetable oil, as vegetable oil doesn't react with iron and rust it. This means that, you are replacing a significant fraction of your body fluids with a immiscible fluid. Furthermore, these iron particles can cause a series of clotting and other terrible stuff to your body once introduced into the body.
TLDR: Use ferrofluids, body starts to spike out and burst, or else blood vessels would clot.
I will always stick to centrifuges and O'Neill cylinders. At least you don't run the risk of feet bursting due to ferrofluid spiking, or blood clotting due to iron particles.