You can replace your one mattress with this pair of matching mattresses in your traditional frame. You would also need another heater (one under each mattress).
For all traditionally made wood, MDF painted or upholstered frame type waterbeds between 8½"(21.5cm) to 9¼" (23.5cm) deep.
Dual Deluxe Mattress Features
Also included is the
For guidance on the type of mattress you need:- in the "Waterbed Buying Guide" above "click" on "How do I choose a mattress".