Some hemibagrus have the personality and are trainable but realistically some won’t stop at 20” their whole life. Some of the girraffe cats again have personality and are trainable, although making sure you don’t get a 3ft one is again not guaranteed.
Liearius are personable and trainable but size will be the issue.
As Victor says, most of the personable and trainable cats tend to be so personable because of their size and most exceed that 20” mark at some point, a number of years down the line.
Lima shovelnose may become personable and trainable with age but not tried with mine and they are not a bulky fish.
Passing on to someone a personable and trained larger fish is obviously easier than passing on a brute or at least on the side of finding a home, it will of course be much harder on you as these fish do become one of the family.
The alternative is something none catfish, such as a giant gourami or puffer.