For functional needs, such as the drawers that would be in the bed base in your project, I'd absolutely use slides for the best long-term performance and ease of use. Traditional wood slides are great in fine furniture for sure, but for this project...metal for me. They can be hidden types so they don't show as a compromise between looks and function.
For the internal rails on the frame that will support your platform, there's no need to eschew wood if you us material that's appropriately sized and use a fastening technique that adds strength. A groove, glue and a few mechanical fasteners (screws) would work just fine. Be sure that the grain direction of the rails matches that of your frames. One thing...you still need center support even with a platform for a king sized bed, so be sure you plan for that in your structure.
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The most expensive tool is the one you buy "cheaply" and often...