Wow! Thank you, both, for these wonderful replies.
Michael, your practice strategy's just what I need to be thinking about at the moment. And I love the point that, if you work through a I-IV-V chord progression in minor thirds you cover all the keys.
Arthur, thanks so much for your supportive and pragmatic advice. Your point about not making practising seem like a chore must be fundamental to progress!
What a great website this is.