I fulltimed in a 22ft CCD for a year, then made an "impulse buy" of a 25 Safari FB SE. I love them both, and have decided to keep the 22ft as a guest house for my family... who have all started to visit!
The smallest NEW Airstream is the 16 ft Bambi, then the 19ft Bambi. I really liked fulltiming in my 22ft trailer, but then I'm single... The couples who advise getting a longer one are giving you GOOD advice. Remember that you could get caught in 4 days of bad rain, or have a vehicle breakdown.
If you have many friends and family who will welcome you to visit, or plan to stay at a resort hotel or casino or other large venue from time to time, you could be all right, but if you're going to do most of your travel time IN your unit, go for a 25 at least. I'd advise looking at www.colonialairstream.com
and viewing their inventory. They actually have a better representative layout of sizes, colors, etc. than www.airstream.com
shows... and they do a good job of keeping their website updated.
Find the LAYOUT you like most first - remember dinettes can be converted to beds but its a time consuming job and you have to make/unmake the bed every time you use it. Think about your lifestyle too when deciding couch vs dinette.
Happy hunting, Happy trails. SYDTR (see you down the road)