most suitable mattress for me and my husband

Many thanks for all the useful info on your website.
Could you please advise on a suitable pocket sprung mattress for me and my husband?
I am 10 stone with some mild pain in my lower back due to a disc problem.
My husband is 15 stone.
We have a good quality double divan base with a platform top and both prefer a firm feel to the mattress.
We have a budget of around £400 and like what you have said about the Origins Pocket 1500 or 2000 sprung mattress.
Would one of these be suitable and which mattress would you recommend for our weight please?
Thanking you for your time.
Susan Brick