A bed is meant to repair and rejuvenate the body. This can be best achieved in a wooden bed.
Metals accumulate electrical charges which distort the body’s own electrical field and do not lead to peaceful and energizing sleep.
Metal bed frames also act like antennae to attract and amplify any radiation in the bedroom leading to disturbed sleep patterns.
Wood is a natural product and the best renewable natural resource. Make sure that you purchase responsible wood from scientifically managed plantations. Once a tree is harvested it can be planted again and it will be available in 20 years. Other geological resources like fossil fuels and metal ores take millions of years to regenerate.