I have never kept such a catfish but there are a few I found from Baensch Atlas that you might find interesting:
Mystus bimaculatus
Amblydoras hancockii
Callichthys callichthys
Dianema longibarbis
Dianema urostriatum
Synodontis alberti
S. schoutedeni
S. notatus
S. eupterus
I've never kept any of these species and I'm not sure of their availability, although S. eupterus and S. alberti don't seem too hard to get and there is a M. bimaculatus on Aquabid right now. According to Baensch, many of these are diurnal and active. All are supposed to be peaceful towards tankmates of size >3 cm.
I'd be interested to know what you decide!