Here’s a great stretch for your quadriceps. Using the wall can help you intensify the stretch - if it’s too much, check out a simpler quad stretch I posted recently! If you have sensitive knees, I would recommend placing something soft under your knee for padding, such as a mat or blanket.
To do this stretch, sit on your knees close to a wall, and place one knee at the bottom of the wall with your shin flat up against the wall. Place your other foot on the ground so you can rest your hands on your knee. You should feel a stretch across the front of your thigh. Repeat on the other leg!