My sister has two dachshund's Rascal and Charlie. Charlie is a long haired miniature dachshund that barely ever gets cold. Rascal on the other hand is almost always cold and because he's got a little something else mixed in there he's a really LONG dachshund. Most of the sweaters that you can find in pet stores don't fit him and so I started looking around to see if anybody had solved the sweater problem. I finally found this pattern on ravelry that you can customize for whatever size you need. Even better is the fact that the price of the pattern gets donated to the Michigan Animal Rescue League.
The pattern is very simple to follow and adjust. It tells you exactly where to measure on your dog and how that relates to the pattern. All in all I think it took me about three days to finish one sweater. The only bad thing is that Rascal doesn't like wearing sweaters. Its almost like he thinks that they're slowing him down, like he can't zip around the house or yard at mach 10. That's why in this picture he's just sitting on the chair all sad because he's been put in a warm and stylish straight-jacket. Can't you just see it in his eyes, "PLEASE get this thing off me, I promise I'll be a good boy..."