Sun salutations. Do five salutations in a row, taking your time, inhaling when you rise and exhaling when you lower. Take five breaths in downward dog pose. (Use cobra pose at first; upward dog pose will be safer after you've become conditioned.)
There are some amazing stretch videos on YouTube – I find beginners yoga particularly helpful. Yoga With Adrienne is who I watch 🙂
When I had a personal trainer we did front back side lunges and toe touches. We did a calf stretches. Arms to the side and neck rolls. Then we began the work out.
I would suggest taking a restorative yoga class to learn many different poses, and then create a routine that works for you. “Restorative” yoga is a specific class to look for.
My advice is to go to a physiotherapist, do a test to determine where are you now, and after that set with him/her a realistic plan (time and effort) of exercises to do to improve mobility.
Start taking deep breaths and rasing your arms. If you can stand you can do this while sitting down. Then lave your fingers and try to take your hand upper. Then inhale and turn right, exhale face straight. Do the same to the other side. You can also do this with your hands on your waist. Then say yes and no with your hañead. Control your movements. And then take your right ear to your right shoulder. Control the movements and count to 5 holding and then get back to normal position. And repeat to the other side. If you want to involve arms and legs I suggest flex and extension. While flexing inhale and then exhale and extend. Arms straight to the front and then repeat while in the air up. Legs first sitting down and then standing if you can.
I use Pilates. You can get a CD or video of a good workout. I got one and did it with the video until I didn’t need to watch the video anymore.