is it your front leg?
Bending of the front knee is part of most bowling actions, and it lets you spread your weight through your action. I would say if you are looking to gain pace that it comes more from your shoulder and wrist, than from your legs?
Height would say more straight back and getting your front (left) arm as high as possible, rather than straighten your front leg. You will also start to feel excess pressure of your left knee if you keep on doing this? (depends on what arm you bowl with)
Squats and Lunges are good for cricketers in general as it increases strength, so that would help?
Could balance those with abdominal stretching exercises as well so like medicine ball sit ups?