I bought a Purple mattress because I thought it would fix my back and neck pain and it has only made it worse. I will also be going back to a more traditional spring mattress soon.

I'd also recommend sleeping on the floor with a couple sheets and pillows. Sounds like it should be uncomfortable, and it is for a bit, but after a while your body just adapts with postures that do wonders for spinal relaxation and relief from some back/neck pains. IANAD.

If a memory foam mattress makes a person's pain worse, how does it do that -- or how does a different type of mattress avoid doing that? (honest question)

The way foam mattresses work is weight deformation. If your butt is heavier than your head, it sinks in more.

I’ve never seen any evidence to suggest this was good for spinal alignment. If you’re a side sleeper, it can also be bad for your shoulders if it doesn’t sink in enough.

My take is that this is good (for me). At least the body can sink.

If you don't sink evenly, your spine is aligned though not level. Whereas in a traditional mattress a poor fit to your body will feel like a hammock, or a hard floor with pressure points

My problem, ultimately, was that my SCM muscles were extremely overworked and felt like I was hiding two brautwursts in my neck - the muscles were so tight that they were pinching some kind of nerves and sending referred pain to my head and eyes. After changing back to a spring mattress the muscles softened and returned to normal and the pain subsided.

I think that since I am a side sleeper (and have desperately tried other positions with no luck), that my body was sinking in to the bed but my head was not and so my neck muscles were compensating to try to "hold" my head/neck all night long, causing them to become overworked and fatigued.

I suspect people who sleep on their back or stomach have different experiences; my wife sleeps on her back and found the Casper to be comfortable but ultimately she got tired of the 'soft' edge of the bed which was not easy to sit on without sliding off, so she shopped for a spring mattress - and once my pain subsided we were able to put the timeline together.

I had the opposite experience.

Been on memory foam since 2011. "Upgraded" to a $3k traditional mattress in 2021. My pain became unbearable after 6 mo. Since my old mattress was disposed of, I bought a $300 memory foam mattress from Wayfair and it resolved my issues.

There are different types of "conventional" mattresses. I had heard that hard/firm is generally better if you gave back pain and bought a locally sourced, extremely firm mattres. The first month sucked. But ever since it's like heaven. It's very thick and heavy and I have no idea how I'll find a replacement, which is probably due here soon.

I’m glad you’ve gotten relief, and really sorry you tried all those other things first. Did you happen to try a latex mattress? They seem “foamy” but they are much more like spring mattresses than they are like memory foam. Basically the more compression it is under, the more resistance there is, exponentially, whereas memory foam compresses linearly. My wife and I switched to Latex and it made a massive difference in our sleep quality and how we feel afterward. The memory foam mattress made us hot and made my back hurt really bad. Now I wake up and I feel refreshed, and I sleep an hour less but get the same quality of deep sleep as before. You may not want to tamper with anything since you’ve found a solution, but I wanted to mention it because it does give more pressure relief than an inner spring but with more support than memory foam. They’re expensive and heavy though.

I have not; we had a spring "pillow top" mattress and I got the Casper on a whim as a gift for the wife, but after a few years she had enough of the edge of the bed being so soft and hard to sit on without sliding off and she shopped for another coil spring mattress. Haven't tried a latex one, but it sounds like possibly a good combination of both, I may investigate that

When I was in high school my mother bought me some ridiculously expensive futon. One of the western ones which are largely just layers of cotton with a thin layer of pillowing on top.

I had other issues sleeping at that time, but comfort was never one of them. And later on, when it became her guest bedroom, visiting home would often relieve my pain in a couple nights of sleep.

Her elderly aunt came to visit, and my mother had the mattress "upgraded" with a 6 inch foam \ pillow topper. I cant sleep on it. It causes me physical pain and distress. Eventually she replaced the mattress too, and now its just a ridiculously thick piece of foam and pillow. My spine relaxes to some kind of crazy bend when I am on it. I wake up feeling like I spent all night in a boxing match.