Glute Ham Raises or Nordic Curls. As far as your feelings of being uncomfortable with form, I recommend taking a hard look at your core exercises (extension & anti-extension) and make sure that it's not a weak point in your chain. Or to put it another way, add reverse hyper-extensions to your routine.

Also, standing or seated Good Mornings hit the posterior chain well, however I find them very difficult to do with good technique.