A mattress insert, able to be inserted into a traditional mattress, includes a plurality of compartments, each containing gel beads and water suitable for simulating the feeling, pressure relief, and temperature regulation of a waterbed. The mattress insert is placed into a foam structural material of the mattress, providing the mattress insert with support and preventing the spread of the gel beads within the insert. The foam core of the mattress may be either solid or rounded. This mattress technology and insert is useful for beds, including medical beds and dog beds, recliners, chairs, and sofas.