I understand the spirit of this comment but I think it’s pretty clear that the person you’re replying to is simply trying to offer helpful advice in fairly neutral tone.

And it is the correct advice. A mattress doesn’t cost less simply because it’s softer it certainly doesn’t cost more just because it’s firmer. Budget aside, there is definitely a degree of personal choice when choosing a mattress.

If you've got a mattress now and it hurts your back then you already bought a mattress with your own money and it wasn't appropriate for you, so you could have spent that money, your own money, not mine, better.