Moonleap meditation wedge supports
We use two wedges instead of, or sometime together with, a mat. By positioning them with the thin end towards the knee and the thick end towards the ankles, the weight of the the legs is taken away from the knee to the legs themselves. This way the knee is still low, but without pushing hard into the floor.
The wedges are obviously much easier to transport than a mat, yet the support given is just a good if not better. Harvey says - "Before using these wedges the outside of my knees used to get quite tender after a day of sitting, but no longer is this the case even after a week long retreat."