Most important, do you want to record the movement from inside the glider, or from outside, or both?
Good results most probably require a combination of both methods.
Just to explain the problems of on board data acquisition: imagine you are the pilot or a passenger, and want to determine the the movement with closed eyes. Your feelings correspond to the information obtained from a 9DOF (accel+gyro) sensor.
Then it will be almost impossible to determine the height, speed and heading of the glider, you'll only notice a shock (acceleration) on start and on touch down, and nothing special in between. In math terms the initial acceleration can be integrated into a speed, which again can be integrated over time into a distance. Even the smallest error in the acceleration will result in a wrong speed and distance computation. The same for the height, where a small decrease of gravity (Z axis) will indicate a constant loss of height. All that only for a straight flight route, with no curves and no wind affecting the speed and heading.
More sensors can be added, like a magnetometer which reports the absolute heading, wind speed sensors for the relative speed, and a height sensor for the relative height over ground. The determination of the absolute speed requires the same sensors at stationary positions along the flight route, at least one when no turbulences are assumed during the flight time. The same for the height, where in the simplest case the height over a flat surface equals the absolute height.
Now it would be helpful if you disclose the exact purpose of your flight monitoring, perhaps there exist better methods for collecting the required information. See e.g. instrument landing system (ILS).