Don't buy this bed unless you like sleeping in a canoe

We've now had this mattress for just over a year and have been significantly disappointed. Specifically, this mattress gives sleeping 'in' bed and 'climbing' out of bed a new meaning. Less than 2 months into owning the mattress, we found that we would wake up in what literally felt like a canoe as we would sink far into the mattress while sleeping. This has led to a lot of sleeplessness and occasional back aches and needing to literally climb up hill to get out of the bed in the morning. Our retailer did send a technician out to look at the situation and he was able to make some adjustments that provided some degree of temporary relief, but 2 months later the mattress has returned to it's prior poor performance. Neither of us are large people, so this is not a weight issue. We believe it's a design fault and will have to seriously think about buying a Serta again.