Keep the lower knee on the floor to support you as you build up strength in the arms and core.
Or instead of stacking the feet bring them apart slightly so that the outer edge of the right foot and the inner edge of the left foot are both on the floor. Or bend the top leg and put the foot flat on the floor in front of you – keeping the lower leg straight as in full Side Plank.
Pressing firmly through the hand will help you get lighter in the upper body. This is the press-rebound effect.
Squeeze the legs together to keep them strong and engaged.