Snow Angels

Lie on your back. Use head support if it feels better, depending on mid back tightness and head position.
Place your hands flat on the floor/mat up by your ears up then slide your arms overhead and back down as though you are making a snow angel.
This exercise is gentle. Do not force it, and do not do this if it’s painful. It should feel good, like a nice chest opening movement.
Roll slightly to the side and do one arm at a time if it feels too tight to do both arms.
You can also start by connecting the reach with an exhale to improve posture, connect to your core, and get the mid back moving.
Do about 10 total or 10 per side.

Cat/Cow

Start on your hands and knees. Your hands should be directly under your shoulders, and your knees directly under your hips.
Inhale and look up while slowly arching your spine, feeling each segment of your spine move.
Exhale and look down while slowly rounding your spine.
Focus on the areas that feel stiff and try to get them to move a little more than the parts that easily move.

Things to watch out for:

Earlier postpartum this might not feel as comfortable. If you have any discomfort in pelvic area or abdomen (particularly if you had a c-section), or any increase in bleeding then do not do this move until about 3-4 weeks postpartum, or until it feels like a gentle stretch.
Start by going from a more neutral to rounded position, and not going as deeply into that arched position. See video.

Lie on your left side with your knees and hips bent to 90 degrees, place a pillow or yoga block between your thighs.