One of my first interactions as a meditator was learning a walking meditation. I was visiting a retreat in this big beautiful wooden room and we learned how to walk the room, meditate and link breath to movement. It was a great way for me to get started. Now I use a guided meditation app call Buddhify and they offer different styles of walking meditation that I really enjoy. Walking meditation may be more comfortable than sitting still if you have a stiff back or neck. Otherwise, a body scan meditation may be a pleasant way to draw awareness to how your body is feeling whilst lying down.
Though you can’t close your eyes this way, maybe you could try listening to a meditation with headphones during a peaceful walk outside. (I‘ve started doing a daily walk or two around some lovely/serene residential sidewalks in my neighborhood. Love how simple and low-impact- yet powerful and therapeutic- walking can be.) Another thought is meditating while wading in the shallow end of a pool or relaxing in a hottub, if you have access to either of those; you would just need to keep your phone safe from water damage of course- whether with a waterproof case, floaty/nearby surface to set it on or separate speaker to listen with. Or perhaps you could meditate with a heating pad, muscle roller, massager.. anything that might actively relieve the discomfort while listening. (I’m sure you thought of those though, and would be doing them if possible. Sorry if I wasn’t very helpful!)
That is tough and I would recommend giving yourself a couple of minutes to stretch gently (dont make it worse!!) I think though that an important part of meditation is to accept all sensations in your body as they are and just observe them, so it's especially challenging when you're in pain but you can see this as a way of stepping out of your body and notice sensations of pain, instead of living in the pain. Turn the distraction into a challenge
Good posture shouldn't hurt, so I would look at how you are sitting. If all else fails, you can meditate lying down, palms up (corpse pose). The Buddha himself had back problems, and would sometimes meditate lying down