We have recently bought one from IKEA. About £250 with pocketed springs, and a memory foam pad on top, which means it can not be flipped over.
First impressions: it's a lot firmer than our old (probably 10 or 12 year old) mattress, but when one of us turns over in our sleep the other one doesn't get shaken around, because the mattress barely moves. We are pleased with it.