Use handcuffs specifically designed for the bedroom.
These handcuffs usually don't require a key and can easily be gotten out of. Check local adult stores or online. Steel shackles are initially created not for your bdsm acts, but for restricting malignant prisoners. Cuffs can result in skin injury or stop blood flow if used wrong.
At all times use cuffs that have double lock feature.
Evade cheap handcuffs, they can jam or become too tight.