ErgoFlex 5G Mattress

been using them for years

they are very good

It's the firmness and zoning that determine whether a mattress is supportive and both springs and foam come in a wide range so going for the same type of material as before is unlikely to help unfortunately.

And supportiveness also varies with body shape, sleeping position and overall weight so what works for others won't necessarily work for you.

Lower back pain could mean a mattress which is too soft under the bum/hips, especially if your body doesn't curve out there much in whatever position you sleep in. If that's the case then I'd be trying the mattresses that are either unzoned or only softer under the shoulders. Possibly the ones that are slightly firmer than average too, especially if you're heavier than average.

Just looked, and it was actually bought 9 years ago last month.  Looking at the website, it looks as I recall.  I think it may have been 10 cm of memory foam then, though.  The key matters are the depth of memory foam and the density, and they were the only company to specify both back then.  There are issues, it is really deep, so if you have a fancy headboard you may lose the pattern and extra deep sheets are needed.  Memory foam is warm, so don't expect to use the same quilt all year.  It is really heavy and there are no handles, so rotating is not easy.  Plus, it will spoil you for all other mattresses.  On the plus side, the mattress cover has been washed every time we rotate it, and it still looks like new.