Type of mattress

I am 60yrs old, 5 feet and weigh about 8st 9lbs. I have rheumatoid arthritis which can cause me pain when lying in bed. I currently have a 2000 pocket sprung mattress which is firm (but sagging in the middle). I use a topper to provide softness. I want a good supportive mattress that feels very soft and have an iron, wooden slatted bed. I love all the info on your site but am still not sure which mattress I should buy. I also wondered if you have a showroom on your site in Manchester? Thank you,
Best wishes
Helen Roberts