Comparable choice to Somnus Regent -Kingsize

So far in our search for a new bed the favourite we've found in our price range in the Somnus Regent Kingsize. Having read around on here and other sites I know that Somnus is a decent brand but I'm a little concerned about their different attitude to spring numbers which makes it hard to identify comparable products. For reference the Regent is a 4,500 Spring mattress with a 550 Spring base.
I'm 14 stone and my wife is 10 stone and we both like a fairly firm feel to a mattress. I tend to move around quite a bit when trying to get to sleep (probably in part due to our very old, very bad mattress) and my wife particularly liked that she couldn't feel my 'fidgeting' when we tried it out.
I was wondering if you have information about the Somnus 'iP Intelligent' pocket springs. With that many springs are they liable to get damaged, does it really benefit the quality of the mattress, how does it impact on the quality of the upholstery? I was also hoping you might recommend one or two other options, including your own, that would be a comparable price?
We were quoted £1,495 for the divan set with another £495 for the full depth Bedford headboard. £2,000 really is out top budget and I'd be happier landing closer to the £1,500 mark for the complete package. This didn't include a topper, which wasn't mentioned by the same man as a requirement for the mattress.
As a final question, my wife quite likes some wooden bed frames she's seen in Next and other home stores. Assuming we spent £500 on a bed frame, would we be able to achieve a comparable comfort/quality level with a £1,000-1,500 mattress which is designed for use with a frame rather than a divan?
As you can probably tell, where lost in all the possibilities - yesterday I had no idea how hard buying a new bed could be! Your website has been extremely helpful, I hope that you can help find a bit of direction in our search.