M.J.
I moved my son from a crib to a twin bed when he was 18 months. We just got the mattress and put it on the floor with a under mattress rail. I told him just like a crib he had to call us when he was awake. I did put up a baby gate in front of his door just incase. However he called me every morning from his bed. He loved feeling like a big boy. So maybe you could skip over new crib and toddler bed to the regular mattress. Unless however you plan on having more children.