Your adjustable bed may be covered by Medicare, but you would have to get a doctor to recommend (and order) the bed for a medical reason. The supplier also has to participate in Medicare, so this may limit which adjustable bed you can purchase with your coverage. Most adjustable beds are sold by the manufacturer, not a Medicare durable medical equipment supplier.
Adjustable beds are not covered by most other health insurance policies but you may be able to use FSA/HSA money if you have a documented medical reason for the purchase.