Premature Mattress Wear

My wife and I are having the most difficult time finding a decent mattress. The last one we had only last two years and started to sag/leave sleep impressions. We just go another spring mattress from Ikea and the same thing is happening after only three weeks. Could my box springs be causing this to happen? I figured the box springs are so stiff that surely they don't need to be replaced, but now I'm questioning whether that is true. I've even tried putting a sheet of plywood between the box spring and mattress and that didn't help. Was probably too late at that point. FYI, it's a king size bed and we're both under 200 lbs. The bed is sitting on a cheap metal frame--maybe that is the problem? I could try putting some 3/4" plywood or wooden slats across the frame, then put the box springs and mattress on top

 

Box spring should have been bought with the new mattress.
It would be like buy a new carpet to replace the 20 year old carpet and using to old pad to save money.
Ikea sells really cheap stuff.
Want one that's going to last plan on spending far more money.

We bought a Stearns and Foster mattress and box spring many years ago. Still like new and super comfortable.

 

Yeah, I know, but I figured for $1,000 it would at least last more than 3 weeks!

I just can't bring myself to spend much more than $1,000 for a mattress, considering you never know what you're gonna get and there are so many mixed reviews. I'd almost rather buy the cheapest mattress out there and get a new one every year.