Not Martha's 2010 tutorial for creating a Christmas tree bauble mobile that looks like an invisible tree is great, simple, and disarmingly effective.
For the top of the mobile I needed something that would allow me to easily secure a lot of hanging points without them sliding around too much. The perfect thing turned out to be a 17-inch steamer rack bought for about $6 from a restaurant supply store (I found mine at Encore Restaurant Equipment in the SODO neighborhood of Seattle). The rack comes with folding feet attached that were easy to pop out with a little bending. Turn the rack upside down and the spots where the legs were secured neatly become four hanging points...
...I used jewelry monofilament secured with crimp tubes to hold the ornaments. I simply created loops at both ends. I made a bunch of different lengths (details on that below). I secured each line to points in the rack grid using lanyard hooks, and hung a basic wire ornament hook at the bottom ends. The lanyard hooks at the top are strong enough to hold heavier ornaments, and because they close they won’t fall off if the mobile is bumped. The basic ornament hooks allow one to easily move ornaments around from one spot to another. My tip to you: Keep the lines as separate as possible while you’re working with them. I spent more time untangling clear threads than doing anything else on this project. It was maddening. After I discovered just how maddening I started hanging them in groups by length from a curtain rod and weighing them down with an ornament to keep them separated, doing this made the hanging of the ornaments go quickly.