Converting a water bed frame to a platform bed is not a very hard project and you will be quite pleased with the result, no longer needing to worry about leaks or electric thermostats or a wiggly bed. You do not need to be crafty or a carpenter. Simply by following a few guidelines, you can convert your bed into a very comfortable platform bed.
Remove your water bed mattress from the frame. If there was a separate thermostat, remove that as well. Next, remove the plastic liner that was under everything. You should be left with a simple wooden framework around a plywood foundation.
Take some measurements. First the depth of the frame, then the length and then the width. Write these all down.
Shop around for the extra stiff foam. You should be able to find it in three to five inch depths and then in sizes similar to king size beds, queen or twin. You will want to fill in the depth of your wooden frame with the extra stiff foam so that when you sit on the side of the bed, the wood does not press into you. If the depth of the frame is twelve inches, then get twelve or more inches of the extra stiff foam. If you cannot find a local store to supply this, JCPenney's sells it from their online site.
Using the same measurements, get enough memory foam for a six to eight inch layer, depending on how much softness you require. You can get a four inch mattress topper pretty inexpensive, buy two and you will have a nice thick cushion on your bed. The online store, Overstock sells this memory foam.
Purchase a mattress cover for the measurements of your bed or larger if it is an odd size. Lay it in the wood frame and unzip it completely. Lay in the layers of extra stiff foam and then the memory foam. Allow about 8 hours for it to air out if it was rolled up and packaged. Using a serrated knife, trim any excess if necessary. Zip up the mattress cover and make the bed as normal.