M.B.
J., Get the fold up seat. It fold into quarters and can be slipped into a plastic bag. I got mine at babies r us. It is compact and portable and great for little ones in public rest rooms. They have something to hold on without the fear of falling in.
At home I have a potty that is also a stool. I opted to train her on that first, then move to the big toilet. The seat is removable and can be inserted on top of the big seat for her comfort. And the stool can be used to help step up the the big toilet with out your help. I throw this in the car for long car rides-just in case.