With no artificial gravity, ships are zero-g in space.
This is true only if a ship is in inertial flight, i.e., not under acceleration (either positive or negative). In ED's realspace flight, acceleration is nearly 100% of the time, with or without FA. The "gravity" vector will be along the inverse vector of the ship's acceleration, which in most cases will chiefly be "Down is at my back" given the way ships are configured. This is much the same as terrestrial atmospheric flight save that the Earth's (or any planet's) gravity well is non-existent in open space and apparently only partially in effect even in the close proximity of a planet. And there would indeed be high-stress
g shifts under combat or other fast-maneuver conditions, much more than "mag boots" could compensate for. While "inertial dampeners" are a handy bit of handwavium, engineering them in any practical fashion would require radically altering the ship's cockpit configuration we're so familiar with, if it could be done at all. So, basically just ignoring the actual consequences of realspace acceleration is the only useful solution for the game. In my mind this does not detract.
Whether there is a "gravity" vector due to acceleration when in supercruise is unclear, seeing as how the nature of spacetime is rather drastically altered. If so it would stand to reason it would also be "Down is at my back," making walking about while in flight somewhat problematic.This problem is compounded exponentially in a jump, it seems, as
everything seems to go rather haywire during a transition. Again, better not to ask such questions and expect "realsitic" answers.