I had the same mattress for around 11 years or even more. I have some shoulder and back pain probably related to the mattress and I don't sleep very well (with that adding the fact that my neighbor's kids wake me at 8h00 during the weekend, my sleep is really shit).
But I'm waiting to move (probably in March or April) to buy a new one because I also want to upgrade to a bigger bed. I'm sleeping in a very small bed (like, single? or twin?) I'm way too tall for it and I feel very restrained with the space I have to move around. I want at least a queen-sized bed. But my room is way too small for that in my current place.
When I move I'll probably take the week off just to sleep. I can't fucking wait.