Replacing a Sealy Posturepedic double bed

I have had a Sealy Posturepedic Ultra Pillow Rhapsody with a sprung edge base for the last 10 years. As the name suggests the mattress has a pillow topper. It has always suited me, even though I have had back problems, until the last year or so but I think it's age is now showing! I cannot find an equivalent current Sealy bed so am trying to decide which bed to opt for.
I am finding my sleep more disturbed and often have pins and needles, even numbness, in one hand during the night. I realise there could be a medical reason for the pins and needles but, nevertheless, am taking this into account when trying to decide on a new bed.
I did think I should have a firm bed for my back problems but, having read through your excellent website, it would seem medium would be more suitable.
I sleep alone, weigh 12st. I do not want a latex or memory foam mattress and intend to keep my existing 10 year old sprung base, which still appears to be in good condition.
Do you think the Origins Pocket 1500 would be my best buy and, if so, should I choose the 2000 spring tension which would presumably feel firmer?