For anyone who NEEDS to:
I keep donor jeans on hand.
Kneel-on-able Knees: cut a patch the width of the front pant leg. Patch should start 2-3 inches above knee, and end 3-4 inches below the bottom of the knee. zigzag or serge the edges of the patch. put the patch on the inside of the pant leg. straight stitch sew it to side seams. straight stitch sew across the top and bottom. straight stitch around the hole, about 1" away. zigzag the hole to the patch.
Other body parts, ripped jeans behind pockets, worn out thigh area. Same. Patch goes inside.
Suggestion for mending your PJ bottom, if they're knit: Use a very soft old t-shirt.