Do You Have a Box Spring?

We've noticed lately that mattresses without boxes are becoming more and more common. Is it because of the price? Comfort? In our experience a mattress with no box spring is not the most luxurious of situations, but that might have been due to other conditions...

Like, say the mattress being on the floor, or it not being very comfortable to begin with. Some companies (like Keetsa or Ikea) say that depending on the mattress or bed frame, a box spring can be superfluous. Have you found this to be true? We'd like to hear your experiences. Do you have a box spring? And do you prefer a bed with or without one?

Image: LivingEtc