I looked into this question a number of years ago, as a side-sleeper wondering if and whether I should try to sleep on my back, which would simplify things considerably. I couldn't find anything worth citing, and concluded either I was looking under the wrong keywords or the desired research doesn't exist. Since my own efforts to try to switch failed, I gave up and bought a real body pillow, which seemed to help.
For some people, side sleeping is the best way to reduce sleep apnea, which can be worse when sleeping on one's back.
Personal experience: I had been falling asleep on my side and waking up on my back. Back sleeping is more comfortable for me. I decided to fall asleep on my back, and it was easy. Then I was diagnosed with sleep apnea. After trying CPAP, I was told that when I'm sleeping on my side my apnea was sub-clinical. The trade-offs made side sleeping the best choice for me. It was not easy to train myself to do side sleeping.
The YouTuber What I've Learned has a relevant video: What's the Best Position to Sleep in? Do we even need a Pillow?
I watched one or two videos of this channel a while back and was impressed by the seemingly solid - but non-conventional - argument (it was on salt intake). I subscribed and was *dismayed* by further videos. I wouldn't put much stock into the either the research being quoted (if you didn't review it yourself) nor the treatment of the research made by this channel.
That being said, I haven't watched this particular video. What it says might all be true.
It seems like this particular video basically says:
In total it says there's no strong evidence but the evidence they reviewed point to side sleeping being better
Personal experience / opinion: For me sleeping positions are an issue of expanded (back) or contracted (side) body language.
In an expanded state I seem to have a lower threshold for cognitive dissonance. I.e. my mind is less prone to indulging in pleasant-but-at-odds-with-reality thought trains. So I, for mental health reasons, try to fall asleep on my back when I can manage to tolerate the expanded state.
Personal experience: undetermined, possibly posture- or prediabetes- related reasons led to myself dehydrating at 10 times the normal rate when sleeping on any of the sides, starting at about age 27. As such: enjoy the variety while it lasts (left side is usually mentioned as more optimal of the two because of the way the liquids in the digestive system are positioned). Learning to sleep on the back did not take much time or effort at all.
I frequently hear the advice that it's better to sleep on the back and worthwhile to learn to sleep on your back. Are there any studies that backup that advice. Otherwise are there other good arguments? Personal experience is also welcome.