In my experience, even unskilled boom-operators take pride in their jobs; in fact, a lot of people really enjoy that job, and they stay on-task. I shot a feature-film, and a few shorts, with unskilled boom-ops, and they never missed one single take. I don't think you should worry about them forgetting to press "record", especially if you follow protocol.
You: "Roll camera"
Cam-op: "Rolling"
You: "Roll audio"
Boom-op: "Rolling"
You: "Slate"
Slate person: "Scene 1, Shot 5, Take 30"
Slate: SMACK!
You: Action!
How can they forget it, when you tell them to do it, and then they confirm that they have done it?
Also, syncing audio is super-easy. I promise, if you're doing narrative work, external audio is F-ing great. Especially since this camera records crap audio.
Which one do I recommend? Well, the low-budget standard seems to be the Zoom H4n (and that's what I use). However, one of our resident audio experts is not a fan of that recorder, because it records at relatively low-levels. I don't remember which one he recommends, though (but if memory serves me correctly, it's a little bit more expensive).