I bought the Hovag medium firm from IKEA about 6 years ago and it's been flawless. Pocket sprung with a thin memory foam top. Think I paid less than £200 for it.
It's since been discontinued and replaced by the Valevag. We're considering getting a new one and moving the old one into the rarely used other bed in the spare room.
Pound for pound the best mattress I've ever had.
Unless you specifically have a mattress labelled 'No turn', you need to rotate the mattress. I am 62 and can honestly say I've never had a hump in the middle, so it must be user error. I have two beds (two houses). My main bed has a memory foam mattress from Next, which is OK. My second home bed has a Hovag mattress from IKEA. I think that one is discontinued now, but they'll have an equivalent. I would highly recommend it. The bed in the spare room also has a Hovag mattress and every guest, without exception, has remarked on what a great sleep they had.
Go to IKEA and lie on a few beds. I am a fellow back sufferer and swear by their now discontinued Hovag mattress. I have one at my second home and it's much better than the expensive memory foam mattress I have at my first home. Valevag and Vasteroy are alleged to be similar to Hovag, depending on how firm you like your mattress, so try both and see what you think.
DevilRenegade
