From Ellen,
What are the dimensions of a daybed mattress & how thick do they come?
Hi Ellen,
A daybed mattress is a typical twin size mattress size (38w X 75L). Thickness is entirely up to you. The only place that you are limited on thickness would be on the trundle if you use one and that would be a max
of 8″ thick.
Daybed is called such because it is narrower than a twin. They are traditionally 30 or 33 inches wide–more comfortable for day time sitting.