Pretty much any brewing supply store will sell them, and I’m not aware of any qualitative difference between them. (You may want to buy one that comes with information that will help you compare your start and end readings, so you can know how much alcohol was produced. Some don’t come with any information. Or, you can buy or download the information separately later.) Every one that I’ve seen is also glass, so I don’t think they’re unbreakable – you’ll just want to be very careful.
Whether or not you need a tube depends on your brewing setup. Basically, a hydrometer is something you drop into the liquid to see how high (or low) it floats. If you can easily reach into your container to grab the hydrometer out again, you do not need a tube. However, if you’re using something like a carboy, with a narrow neck, it might be hard to reach in there. ;) In that case, a tube allows you to use the hydrometer without having to put it right in your vessel.
Using the tube (and not dropping it right in the batch of hooch) also helps you avoid contaminating the whole thing with any nasty bugs that might ruin all your hard work (such as acetobacter, which will turn your alcohol into vinegar) if the sanitizing wash wasn’t 100% effective.