I used a potty for my first daughter, but for my second I used the seat that goes on the big potty and actually liked it better. Also, it seemed easier on my daughter to not see me clean out the potty. I suggest using the seat you have, since he is used to it and likes it and get a step stool for him to use to get up and down.
If you do opt for a potty, the brand/style/kind doesn't really matter. It does not need to be musical or highly decorated, just functional. No need to encourage your little guy to PLAY with it. Yech!