there is a thin 2nd floor available in the catalogue, if that helps. its a lot thinner, and when placed, sits at the same level as the top of the normal floor blocks. the downside is its the same as the wooden stairs, so its one colour only.
also, they just added height to the build boxes so you should be able to squeeze in another block or two for floor.
i found (befor the height-box update) that 5 blocks tall was enough so that the area registered the furniture in both the ground floor and first floor.
as an alternative, you can use the thin wooden roof tiles as floors too. there are black and brown variants in the catalogue aswell. they look modern like laminate floors hehe
(and yes, i would also like more flooring options in mod form, but till thats here, hopefully, this might help)