As a thing in daily life we humans end up sleeping on mattresses so why not add them to blockheads? (Albeit not comfortable.)
Crafting recipe is simple:
50 iron springs
Iron springs can be crafted in the metalwork bench for 1 iron ingot, you will get 5 iron springs from one ingot.
Mattresses will ensure your blockhead gets a better sleep, but it may also start being required for beds.