Why does one mattress with MicroSprings feel so different from one with a pillow top?

Edelman

I recently bought the Silent Night Milldale mattress.  They offered it on a 3 week trial as it is not in any stores.
I also tried the Loren Williams Comfort mattresses.

Silent Night has all the pocket springs, plus a layer of microsprings, then some layers of natural fibres.  Looks and sounds divine!
The LWs one has the base pocket springs, and then a later of Microsprings wtih other natural fibres.  Same - looks and sounds divine.

The SN one that I bought is NOT divine.  I got the softer feel one, and while it has 'give' to it, when you lay on it, it's like laying on a bench where the wood 'beams' down (bit like an old Pram's suspension), and you get that bit of softness on the top.

The LWs one, lay on it and I swear it feels like instant memory foam (it isn't), and is cossets around all your varied body shapes, on your back and your side.  Far more cossetting than the SN one.

So one would expect the SN one to give me back ache.  It doesn't.  Not a bit of it.
My old Rest Assured one had a similar setup to the LWs one, and I got back ache from night one of using it.  And thereafter for quite some time.

This is why I am so confused.  Surely a softer more cossetting mattress should be comfy and "mmm yeahhh that's nice".
Why would a firmer mattress that doesn't seem like it supports me, not give me any back ache?!

How can these be so different?  Is it the very top layer of the SN one that doesnt' allow the springs to form around my body nearly so well?

https://www.silentnight.co.uk/rest-assured-milldale-3000-pocket-wool-mattress.html
https://www.lorenwilliams.co.uk/sienna-comfort/

These are the two mattresses.

I'm stuck on what to do.  And in fact why they feel so different, when the facts should be the opposite.

greensalad

I find on softer mattresses that it gives me back ache because I fall deeper into it. A firmer mattress may not feeling like it's supporting you but possibly it's aligning your spine better and therefore, despite not feeling instantly "comfy" it's better over a full night's sleep.

kdotdotdotdot

The theory is that for bad backs you need a firmer mattress type because firm gives more support, rather than letting your back sink down into the mattress, which is what happens without enough support.

If you find the SN one comfy and it doesn't give you back ache, then you're on to a winner.  If it's not comfy, then it sounds like you need to keep shopping around.