My wife and I almost got a Sleep Innovations mattress, but in the end we felt that we couldn't buy a mattress that we hadn't had a chance to try out. We both like a very firm mattress, which can be difficult to find.
While it's true that lying on a mattress for a few minutes won't tell you whether it's the best one or not, it sure did help us rule out many mattresses. We ended up getting an Ikea mattress, which turned out to be quite nice.
Ikea also seems to be the only place in the UK that sells decent slatted frames to put under your mattress. I guess British people aren't familiar with the concept.
Ah yes, we previously had a box spring but opted for the slatted frame. I like it a lot, and I like having the bed lower to the ground (although the best my back ever was when I slept on tatami for a semester in Japan)
While it's true that lying on a mattress for a few minutes won't tell you whether it's the best one or not, it sure did help us rule out many mattresses. We ended up getting an Ikea mattress, which turned out to be quite nice.