don't get an instrument on the basis of it needing to be quiet around people, get it for its sonic power and beauty. 1000 years ago in my student days, i put socks in the f holes and practiced quietly when roommates needed quiet time. i still got all the work done that i needed to. also, you'll need am amp for anything you get, anyway. i say try to find a good 1/2 size plywood in good shape. you'll love the life-journey a double bass takes you on.
Like I said, a lot of my problem is that I just don't organize my practice time. I have the time to play as loudly as I want, I just don't make good use of that time.
I used to do the socks in the soundhole thing when I played a lot of acoustic guitar too. It got the job done.