let us know the dimensions of your tank cos this is important, as the predatory pims have long barbels and would be very unhappy in tank with les than 30" width in my opinion.
they barbels waste away and it spooks them if they keep touching the tank sides.
lima shovelnoses are great but they are no good with aggressive fish as they dont suffer stress well.
girrafe nosed cats adult size ranges from 18" upto the biggest ive ever seen which was at least 3ft long. they really seem to vary in size.
Pimlodella blochi and pim clarias get around 10-12 inches, they would be ok, but probably be expensive as they are rarely on import lists.
How about a clarias cat they get 16" but are very territorial and probably wont share the tank bottom with other cats. Also will swallow small fish.
how about a shoal of pim. pictus they are great and get to around 6", very active and colourful.
meg. irwini gets quite big around 2ft