Advice on which base to get through restricted space

Hi
I need to buy a new single bed( thanks for the comparison chart you e mailed me) and my bedroom is in an attic with a very small narrow twisted staircase to it. I won't be able to get a divan base up there or a large frame and was thinking of getting a smallish slatted base with foot and head board but have read comments on mattresses not being supported enough with slats.
Can you give me any advice on this ?
thanks