Millbrook replacement – Artisan Bespoke 004?

Follow-up to an earlier post.
I am looking to find something similar to an old standard tension Millbrook pocket sprung mattress. I have tested some of the existing Millbrook range at Furniture Village and I think their standard tension hasn’t changed over the years, but it is significantly firmer than many other manufacturers’ medium or standard, which I have found to be far too soft.
Whilst I don’t get on with springs that compress too much (when you sit up in the morning and your knees almost touch your chin because you’re sitting in such a dip) I do like to sleep “in” the bed if that makes sense. I have always used a wool fleece topper and whilst I’m using the very firm open coil spare bed I’m also using a 3″ down & feather topper beneath the wool. But I’m getting a better night than on the medium sprung too soft Windsor Bed Co Chatsworth that I’m replacing. back pain has gone.
Given my increasing aches & pains, latex sounds really attractive but I’m a hot sleeper so I’m not sure it would work for me. Currently I’m only able to sleep on my back – shoulder discomfort then numbness if I’m on my side for any length of time. Advice welcomed – I presume a wool or cotton mattress topper might help with the heat but would I lose the pressure-relieving benefits of the latex?
If I go the pocket sprung route I will be replacing with a zip & link version as I am no longer able to turn a 5ft king size mattress. It has been suggested that z&l come up a little firmer than the same size as a single mattress. I am considering the Artisan Bespoke 004 as I’m trying to avoid synthetics. I weigh about 10 stone but prefer a slightly firmer feel to the springs than my weight would suggest. I’m 5’8″ tall. I will continue to use a wool fleece mattress topper – may even treat myself to a new Devon Duvets one.
There is no partner to accommodate in the same bed. What spring tension would you suggest in a king size zip & link (on a sprung base)? And what depth is the Artisan mattress please (and any latex ones if I should consider them)? If too deep I might have to change to a slatted base, might this mean I should be looking at a different spring tension?
So many questions and I sound completely decrepit. Budget is whatever it takes, but I want to get it right.