New Mattress Advice

Firstly, thanks for a very informative website!My question, with enough background (I hope) to be helpful...I have had my present mattress for 11 years. I recently came back from being away at a holiday cottage, and was struck by how uncomfortable my mattress is in comparison to the new mattress in the cottage, and so felt it was time for a new mattress...Some details about my current one. It's a Sleepmasters Back Care Supreme, and is pocket sprung. (I think it was purchased from Bensons) I recall when I bought it I tried memory foam ones, and didn't like them, and wanted another pocket sprung model. I find *firm* mattresses most comfortable, and recall being advised to get an 'ortho' model. Certainly don't like softer mattresses.I'm just over 12 stone, and 5'10''. My bed is a double.I'm also looking to get a new base.Budget? Well, normally in life I take a 'quality first' approach, and would hope my new mattress would last 10 years. Would rather get a quality product than a cheap one--which normally means paying extra.Thanks in advance for any advice you can provide. Greatly appreciated.