Great idea, but I agree about the mattress on the floor for a while first. Also, since he's co-sleeping, you may want to transition slowly at first. It's in your best interest to keep all nighttime parenting as pleasant and peaceful as possible. What worked for us (my daughter was 14 months at the time):
She was still nursing, so I'd nurse her before her naps and lay her down on the mattress on the floor. This helped her get used to waking up in that position.
A few weeks later, we started letting her go to sleep at night in her own room. Again, we were still nursing, which really helped. We would lay on the mattress together and she would nurse to sleep. When she woke in the middle of the night, I would bring her back to the family bed, nurse, and we would stay there the rest of the night.
At 18 months, we weaned her from night feedings, but we still let her come to our bed when she woke in the middle of the night.
At 21 months, she would still wake in the night, but now we stayed in her room to sooth her back to sleep (songs, patting, back rubs). We transitioned to a twin bed (normal height) around this time too.
At 24 months, she miraculously started sleeping through the night. She has never returned to our bed (except for tickles in the morning). She has medical issues that I really thought would prevent her from EVER sleeping through the night.
I know some moms think we're crazy for going so slow about nighttime issues, but it worked for us. And now my daughter has wonderful bedtime habits and has never had a problem getting up at night to use the bathroom by herself. Everything about our nighttime is positive, for the whole family.
Good luck!
-K.