Who makes a 3/4 mattress that can fit up a very tight staircase to our third floor?

Nine Clouds Beds does!

It has to be made without springs because that type of three quarter mattress bends more easily and  is way less likely to get damaged by bending.

Our Blue Sky 100 3/4 mattress fit the bill perfectly for tight entrance spots to bedrooms and it can even come vacuum paccked in a box.