I may be a bit late to the party but I'll throw out a Ruger SP-101. I have one and love it. 8 rounds of "make-them-cans-dance" fun! It is smaller than a GP, but offers the same DA or SA experience.
I shot mine for a while, then smoothed out the action following this guide:
https://www.kevinsworkbench.com/sp101trigger/index.html
I later worked on a couple of my other SP-101's using this kit and it worked like a charm:
https://www.mcarbo.com/ruger-sp101-/-gp100-trigger-spring-kit.aspx If I were to be doing another SP, I'd use this kit. Has all you need to smooth and lighten the action.
The M*Carbo kit would make a good Father-Son project. It has great instructions, isn't complicated, and doesn't take long. A good polishing of the internals coupled with a reduced power hammer spring made all the difference in the world. I chose not to replace the trigger return spring as it did not seem to make enough of a difference in my guns to matter, felt too mushy and made trigger reset slower.
Best wishes to you and your son on your quest!