waterbed that typically looks like a conventional spring mattress. It will normally have a zip on cover with thick foam shoulders on the inside. These foam shoulders hold the mattress in place. So if you’re looking to replace your soft side waterbed mattress, it is very important you don’t get a mattress that is designed for a hardsided style of waterbed. Soft Side waterbed mattresses are specially made to fit a softsided waterbed. Likewise a hardsided mattress is designed to fit a hard sided.
Now you are sure you own a soft side waterbed mattress, this page has five different stabilities to choose from. The ST1000 for example has lots of gently water movement all the way up to the ST5500 which has very little water movement. You want to decided where you come on that scale of 1-5 in terms of waterbed movement. If you need more information on the mattress stabilities. Click on each picture and that page will tell you all about that mattress.