The best thing for an achy back is tennis balls. All you do is take an old sock and put two tennis balls inside. Then tie a knot in the sock, making sure the balls are as close together as possible. (I'm sure there is fancy massage tool that does the same thing, but why not go for cheap.) Then whenever you feel tension coming on, or just when you're watching TV, lie down on top of the tennis ball sock contraption, placing a ball on either side of your spine. The gap between the balls creates a space for your vertebrae, while each of the balls massages the muscles on either side. Relax onto the balls and feel your tension release. After a few minutes in one spot, move the balls with your hand. You can also roll around on top of the balls for a deeper massage. It feels amazing and it's great for people who work at a computer all day. A chiropractor taught me this one and since I started doing this maintenance on a regular basis, I haven't been back. Sorry Doc!
Shiatsubags are easier to use, and much more functional. The bag has multiple high density EVA 3.5-4" balls that are lightweight, odorless, and have a smooth surface so they roll around with no inter-ball surface friction. The bags allows you to roll in any direction and provides a support platform for the body. It also will mold to the contours of the body and to the surface it is used on sucha as a bed, sofa, chair, or the floor.