Good suggestions here! Finding just the right Airstream is a "big" job... but it can be done! Sounds like you have been camping and know what kind of thing you are looking for. I would suggest, however, you read through the thread at this link. It may come up with some ideas for you to consider that you haven't thought of.
I might suggest, however, that if you look at vintage (which I love, by the way...) unless you find one that has been restored, or that one in a million stored its lifetime in a heated/airconditioned garage... you will probably face some restoration costs. If I had to say one thing that is the most to look for... it is the floors. They rot out. Replacement is a big deal.
Good luck! Hope to see you on the road 'streamin by!
Mrs. NorCal Bambi (traveling in S Tardis)