It sounds like cocker is the way to go here. The parts are cheap, there are lots to mess around with, you'll learn how to time them if you haven't yet, and you can set it up however you want. It doesn't take any milling or modification, and when you're done it should be pretty reliable. There's a dozen of every kind of part, and fun to just mess around with on the bench. Once you know how to time a cocker, or even just how to set it and walk away, you're set. You can mess around for while with parts and a set of wrenches and be happy.
Mags aren't tinkerers guns for a reason. There's just not much to them. In most cases that's not a bad thing, but for the OP's purposes, I don't see it as what he's looking for here. And if you haven't shot a nice slider yet, I'd recommend giving them a try. They're different than any other trigger out there.