It depends on your personal preferences and the specific mattress you are considering.(if you can truly sleep on anything then online purchasing is not a bad idea). Online mattresses can be a convenient and cost-effective option, but it can be difficult to try them out before buying (it's usually impossible to try them out before hand and even if free returns are offered they are very cumbersome to arrange). It is important to research the brand and read reviews to ensure that the mattress is of good quality and will provide the support and comfort you need. (There's nothing more personal than a mattress purchase (well maybe a pillow choice) so it's certainly one item that asking friend about makes little sense, the same goes for reading reviews because the writers are not you). Additionally, consider the return policy and warranty before making a purchase. (100% true if you're going to go this route).