av, do you trust my experience?
here's a advise to all newly weds and new parents.
get 2 single mattress. put wooden boards on the floor and lay both
mattress side by side on the floor.
King size sheet set will fit both single mattress.
And when the baby needs to be near the mother sleeping. At least
with the mattress on the floor, you wont have your child rolling
off the bed and hurting themselves.