Deuce5150
Hello & Welcome to the Forum!
Doesn't it feel good to get out that train, smell the ozone, hearing the wheels go clickity clack,
 as she goes roundy round...
I would suggest a Post War 2046 4-6-4 Hudson, to replace the Scout type switcher in your set.
They can be found very reasonably in good condition and will pull enough cars to make you happy.
 Should be able to find one priced $100+/- area, maybe even less.
There are other locomotives available, but for the money, the Hudson is a good choice.
You will be able to use your transformer with it, instead of having to upgrade to a modern Transformer

Happy Rails!

Dave