I'd go the cot and even the cot over a bassinet (as they tend to grow out of them quickly). I say cot because if for there day naps they are at that rolling stage then with bed they role straight out...have personal experience with this when I found DS rolled out of the side carted cot and was face down between the small gap of the cot and our bed. He has also rolled out of bed. So it feels safer if they are in a cot at this stage. I've actually lied down in the cot with DD to get her to sleep so for me the size of the bed didn't matter lol but I'd go cot then bed at later stage.

P.S: doesn't matter what you plan or arrange there will always be something you change once Bub is here haha and I've had to change things both times, so don't stress the small things.