Not sure what your budget or space limitation. You answered my thought since I stand to cut and sit to sew need two different heights. You may still want them slightly different heights. But agree glass top is not the best option.
However since you are sitting, what depth of cabinet do you need for that side of the L since you may not reach the back side or you can use it for storage containers. Or is the L going to be something you can access from both sides is another consideration. I would look for something that is sturdy enough to deal with the vibrations from your sewing machine.