One of the limitations to human space travel is acceleration limits. We'd really like to just shoot spaceships out of a cannon to 99% the speed of light, but the resulting pressures on the human body would crush them. Even for rockets, greater acceleration is more efficient.
Notice though that the problem is pressure: if the entire body is accelerated at the exact same rate, this feels the same as weightlessness. That's why floating in deep space and floating in orbit feel the same.
So a potential solution is to just accelerate the entire human body at the same rate. If your spaceship is accelerating at $a$, instead of pushing the human through their skin, use diamagnetic levitation to accelerate their entire body at $a$. (If you want to simulate the experience of earth gravity, use enough diamagnetic levitation that we would accelerate to $a - g$. The remaining acceleration caused by being pushed against the back of the spaceship will induce the same internal pressures as the ground on earth.)
However, there is a catch: although diamagnetic levitation can affect every location in a region equally, it does not affect all materials equally! In particular, $O_2$ is not diamagnetic at all!
So my question, how much acceleration from diamagnetic levitation can a human handle?