Previous solution:
loo, loop, loops, loos, lop, lops, oops, ops, polo, polos, pol, pols, poo, poos, pool, pools, sloop, slop, sol, solo, sool, sop, spool
loo, loop, loops, loos, lop, lops, oops, ops, polo, polos, pol, pols, poo, poos, pool, pools, sloop, slop, sol, solo, sool, sop, spool