Japan's perceived culture in the rest of the world is really odd. It's this tiny little fringe part of the society that somehow came to be viewed as really mainstream by the English speaking internet. That kind of stuff is viewed as being about as normal as Furry culture is in the West. It exists, and there's a lot of content made for it, a big presence on the internet, but it's hardly 'normal' or everyday. You'd never find it unless you went looking for it in very particular places.
There might be a few shops on Rakuten that sell 'totally for use on your back or something' massage tools, but that's about the most 'adult' thing you'll find on there. Body pillows, hentai, that kind of stuff, is usually sold in seedy brick and mortar stores, specialized internet shops or at conventions.