I have to stretch daily because of my Rheumatoid Arthritis and fibromylagia. I use a combination of stretches from a variety of sources that work for me. A lot of dance stretches from my dancing days. Some stretches are yoga poses, but I do not hold them the way a yogi would, I just use them to stretch muscles that would otherwise be tight. I also use a few different stretches from track and field, and things I read in a book, or read on-line.
I had a friend recently trying to sway me to the dark side, and it was a preliminary to true Hindu yoga. I told her I appreciated her caring, but I was not going to do the meditating on Omm or anything but the word of God. As for the poses, they don't suit my physical needs.
A few years ago, my unsaved sister was also trying to convert me to Hinduism through yoga. (Yes, it is a big way to pull people into Hinduism!) She argued with me for months, telling me all the physical and mental and spiritual help it had been to her, especially since her bad car accident.
I was quite amused when she phoned me up one day in a fit of anger. Turns out her "holy" yoga teacher had been seen in a parking lot stealing a car space from a disable person, AND cursing at them. It was a good door to speak about how when you try and become perfect in your own power you will always fail. Only the power of the Holy Spirit can transform our lives.
I am happy to report she never went back to yoga, but sad that she still has not believed God for Jesus sacrifice on the cross, to the extent of telling me Jesus is a myth. Sigh!
I don't recommend yoga to anyone, unless they need a specific stretch for some physical reason, and nothing else would do the job. But not a whole class or cultivating a practice of it.
You are walking through an open door to Hinduism. And even if you start with the so-called "non-religious" yoga, they will take you step by step into the yoga that is true Hinduism, or a form of demonic worship.