Recommendations for A Larger Couple

Hi, I was wondering if you would be able to advise.
Myself, and my partner are looking to purchase our 4th mattress in 3 years. We have previously had two faulty, and one that just did not cut the mustard so to speak, with excessive sagging within about 6 months.
Our best mattress in terms of comfort was a 2000+ springs/" title="pocket spring">pocket spring, with latex top layer. A Pure Sleep brand mattress, called Symphony, from Oak Furniture Land, which I believe they no longer stock.
Not only are myself and my partner not light, currently both being approximately 20.5 stone each, but due to multiple none weight related health issues , including a spinal issue that I have, we require a firm mattress, but I cannot tolerate anything tufted as the tufting seems to exacerbate pain caused by my health issues, and at the same time anything which conforms to my shape to much has the same effect.
We have tried various mattresses at High Street retailers, and the front runner so far appears to be a Salus Ortho Firm Viscoool mattress from Bensons For Beds.
I was wondering how your Resilience range would compare?
We have a super king size bed, and intend to keep the size the same.
We are also looking at a new bed frame, most likely from a company called Get Laid Beds, meaning any mattress we buy will most likely be being placed on a solid hardwood (Oak, Beech, or Cherry) slatted base, as unfortunately due to mobility issues, a divan, which we have generally been led to believe gives more support, is not an option due to not always being able to control and manoeuvrer my feet properly.
We are at the point that within reason cost is not an issue, as long as the mattress is comfortable.
Any advice would be much appreciated.
Thank you.