Unfortunately, each mattress place can have a custom name put on what is basically the same mattress as his competition, without changing any of the components, OR, they can have several things customized in little or big ways. Makes it damn hard to comparison or price shop. Definitley climb on the mattress and try it out in the usual sleeping positions you use. NO, having sex is not usually allowed on the test mattress...
Keep in mind, that all mattresses will eventually form to fit your body some. OK, maybe youse tiny people don't even make a dent, but us "full grown" folks sure do...
This is KIND OF yet another place where you get what you pay for, BUT, you gotta shop wisely, because it's also another place where you can get screwed badly. If you're married or live with a "significant other", be sure to take him/her along, because it has to be comfortable for both...
There's a place in the SF bay area (Berzerkely) that custom makes some of the most comfortable mattresses I've ever seen, but they are spendy! (european sleep works) size was $2000...just a bit more than I wanted to spend, but I've regretted being so cheap a few times. (only spent $1400 on a Cal King) Still a decent mattress, but no where near as comfortable, nor as well built.