On the other hand, don't discount cheap ones simply because they are cheap.

I got my old memory foam mattress from Woot. It made me sleep so soundly that after a couple years, I started waking up with back pain. Slept all night, but woke up in pain. Gave it to my Mom (best sleep she's ever had, too) and bought a hybrid from Ikea. Still way better than any other boxspring mattress I've owned, and ridiculously cheap.

So yes, they are worth investing in... But that doesn't mean you have to pay a lot.

Sadly, I cannot find an Ikea chair/couch that's comfortable. Still working on that purchase.