Two adults on the sofa bed in any DVC property is a miserable proposition. Much better to get a regular deluxe room with two queen beds. You would be fine in most any deluxe room (other than Wilderness Lodge and Animal Kingdom Lodge) that has two queen beds and a day bed -- you can have five people plus one child under three, which is exactly what you have.
We tried as two adults to sleep on the sofa bed in a one bedroom at Beach Club Villas. The sofa bed sank in the middle. We had them bring in a new mattress as the first one was really lumpy but it only helped a little. We still both rolled to the center and sank. Also, the sofa bed, when open, had horrible bars on the sides that one had to lift oneself over in order to even get out of the thing.
We were so miserable, the four of us (2 adults and two 15-year-old boys)
checked out early and went back to Portofino Bay Hotel where we could have two queen beds.
We would never consider a DVC stay again for four unless it was in a two
bedroom so no one has to "sleep" on the sofabed.
As far as I'm concerned the sofa bed really only works for small children. Even
then, the setup is silly. The parents can't get up and go to the kitchen to get coffee and do some work without waking the child in the sofa bed in the living
room. We found we much prefer staying club level -- the parents can go to the lounge for coffee and work while the kids sleep in. Works better for us by far.
We just returned from a Yacht Club club level stay and thoroughly enjoyed it. Beach Club club level is great too. Even larger rooms are available at Grand Floridian, Polynesian and Contemporary.