bathroom sub floor
 

How would I put a subflood down with just joists?

You want to use 5/8 plywood or better tongue and groove flooring with a tube of floor glue and screws. Do you have floor joists on each side to screw the floor to?

What are your plan with your floor? Tile, vinyl?
I think Neal means advantech T&G 5/8" or 3/4"
Which is the best method for any subfloor.

Let use know what your doing you gave us a really open question.

Thanks!

You might try getting tile up, but I think you will be taking up the old bed up too. The best is to clean off old plywood and start from there with new subfloor. Cutting out old floor is tricky as there not often floor joists on the sides where you need them.