Which “big boy bed” should I buy my 2 year old?

We need the crib for a new baby coming and so we’re looking at buying another buy for our son. I’m worried because he is the type that is very much used to his crib to sleep. He literally will not sleep anywhere else - not on the couch, car, in my bed with me, etc.

Should I buy a toddler bed? Twin/double bed? Twin/double floor bed?