Best stretches for a bad back?

Hamstring and quad stretches. Lying on back with knees into chest and support for head of neck won’t allow for it to happen comfortably.

I have stretched and "moves" and exercises from my Physical Therapist for my neck and back. I have significant problems with both.
I think it's best to get that type of advice when dealing with something as delicate as a bad back.
Good luck.

Sitting in a chair place an ankle on the opposite lef and lean foward as much as possible and hold for 10 seconds, repeat with other ankle.
Touching toes as standing or even sitting.

With the legs opened, go down with the upper part of the body as if you were touching your feet. Feel the weight of your body. Then extremely slowly, as if you were pulled by a string, pick up and stand for a few seconds with the arms opened

Warm up! Even if it’s walking to & fro through your house. Start out slow and don’t push yourself. Even if you only make very slight stretches the first few days or week. It’s not important to bend allll the way over, it’s the movement that counts! Slow & steady!
If your back is really hurting the next day, you’ve done too much. Just take your time and enjoy the journey!

If you’re able to walk, that is the first and best thing to do. Once your circulation is up and your muscles have relaxed, I highly recommend looking into yoga poses, unless your doctor prohibits this.

Surely torsions! Check some yoga on Instagram (marta_sprea), I have a morning routine for my back that I try to do every time I spend too much time sitting or when I feel my back stuck!