We got given one (a secondhand one) - just a basic no-frills one-piece potty - and it was great.
We didn't use it for long though because then DD just wanted the toilet!

I would recommend just something simple - we also had an insert thingy for the actual toilet - and that was used for much longer
I don't think you need one with all the bells and whistles - but thats JMO

PS good to have you back!