Are you looking to change your mattress?
Before you spend over a $1000 on a new mattress, please try a simple camping airbed that shouldn't cost more than $20 perhaps $30 if it comes with a pump. But don't get a big double size one because having a bigger airbed is just wasted air you have to deal with. A simple queen size 8" thick mattress is all that is required to ensure proper flotation. You can make the airbed as firm as you like and or as plush as you like, but don't expect to get it perfect the first week as the vinyl has to stretch. But once that occurs you will have years of sleeping on clouds and wake up in heaven. You will also laugh at all the dopes who spend thousands making Sit&Sleep rich.