Violin is a good one, hard work esp at first but a lovely instrument. It's very portable!
Portability is key? I'd rule out cello/double bass/large brass - yes, they're portable, but they're mega heavy, and cello/bass are also bulky. (in my limited experience I have yet to pick up a brass instrument that hasn't felt heavy, but I guess cornets etc are less so!)
And it's not too late... never too late! Check out the Adult Learners' Forum
Something that inspires you and that you will want to play enough to get past the beginner, "Oh my word is that horrible noise me??" stage is imperative IMO.
edit: if you have friends who play or teach any instruments, or any possibility of trying different instruments, that might help too.