Replacement for old Sealy Posturepedic bed

Hello
We have a Sealy divan bed which is older than I care to admit, but we would like a new bed and divan base.
It's label reads: Sealy Posturepedic Ultra Luxe Crown Jewel Extra Firm with a Torsion 2000 sprung base.
I weigh 71kg and my wife weighs 57kg. I think we both tend to sleep on our sides.
We had a fruitless morning trying many mattresses in John Lewis. We tried mainly pocket-sprung mattresses, but none felt sufficiently "firm" to us. This included several Vispring and John Lewis mattresses at a wide range of prices that were labelled firm. One John Lewis own brand mattress, also pocket-sprung, felt like a brick and that isn't what we're looking for either! (We tried one Tempur mattress and we really didn't like it)
I would describe our old mattress as feeling that we're lying on top of it rather than sinking into it, but it doesn't feel hard, it feels supported.
Are we looking for the impossible? Are we misjudging the firmness?
Would you be able to say which of your beds might be suitable for us?
We don't have a fixed budget, but we will pay what it takes, within reasonable value, to buy a bed that we like.
Thanks for your help.