Inhabitants of another planet (their biology is yet undefined, and if helpful to solving the problem, suggestions can be included in the answer), have a spaceship in which they plan to accelerate to 0.2c over a two earth year period. Technology level is more or less undefined as it's an alien species who can have whatever tech is required.
Of course, F = ma means that the force of accelerating at 0.1c per year is still a big number, even for an entity that weighs something similar to ourselves. 0.2c is important as anything above this tends to incur significant time dilation, and any slower will mean too much time elapsed to reach their destination.
So my question is, How can I prevent my space explorers from being crushed by the acceleration? The parameters of time and final velocity are set and critical to my story, so can't be altered. I'd prefer a feasible but not necessarily completely hard science answer. If there really isn't any way to do this, then a plausible hand-wavy answer would suffice.