I wonder if it's actually better to buy online. Firstly you get something you've researched, not something the salesman pressured you into buying by claiming it's the mattress they have at home as well. Secondly, most people end up buying too soft beds, because it feels nicer when laying down and testing for a minute or two compared to a firmer mattress. Avoid that online.
Really, though? I feel like part of the whole scam with online mattresses is that the review sites where people think they're conducting all this independent "research" are mostly in on the racket, getting freebies and kickbacks and taking payment for top recommendation spot, etc— Fast Company had a big expose on this a few years ago, but they're far from the only ones who have tried to blow the door off it:
