Find videos that you enjoy. Start short and simple with 10min morning yoga or 5 min yoga stretches you can do in bed right when you wake up. If you start to get bored with the video or stop getting excited about it find a new video to keep interest.
To make this transition easier, get an application on your phone that will send reminders every morning to do your yoga session and will allow you to tailor the session to your needs and abilities. DownDog is one of such apps. Notice how you feel at the end of each session, chances are you will feel such a huge rush of feel-good chemicals, you will yearn to have another session the next day. Take note of your strength and flexibility progress after each session, this will ensure you see not only the mental benefits, but will get hooked on the immediate physical progress too. Good luck!
Try a 30 day challenge or something similar. This can really help on days I struggle with motivation I may just do 10 minutes just to keep the habit chain, and then go back to the longer ones when the motivation strikes again.