In terms of scientific studies, an industry-funded 2006 study by researchers at Oklahoma State University (funded by the BSC)  of 59 people with poor sleep who received free new replacement mattresses for their existing mattresses 5 years or older (average age years) found improved sleep, particularly when the existing mattresses were cheap.  A follow-up paper by some of the same authors with additional statistical analysis reinforced these conclusions.  The BSC has subsequently cited this study in the ISPA-published news magazine for mattress manufacturers, BedTimes , to advocate a more frequent replacement cycle, specifically to "consider replacing a mattress every five to seven years"; the recommendation is based largely on this study.  
Loom & Leaf looks the most like a traditional mattress out of the four. It’s all stitched together, unlike the other models we tested with zip-off covers, and has microsuede around the edges and built-in handles on the two long sides — the only mattress to include them. We suspect this is because the Loom & Leaf doesn’t come vacuum-sealed in a box, and the handles help with transport. But anyone who has ever moved will confirm how useful mattress handles are; it’s not like you can re-box up the Casper, and even if it’s only 71 pounds to Loom & Leaf’s 93, it’s no one-man project.