I'd just like to again thank everyone who posted, and give you a quick update on how things are going, now that I've had a couple of nights to experiment.

For starters, the main points I've focused on are getting to the net early, and making effective use of my smashes, which really should be more of a weapon for me.

Starting with the latter, I think Paul hit the nail on the head when he said:
“4) Develop your movement as this seems to be the cause of your smash difficulties in singles.”
Moving backwards is a bit of a weakness for me. I would often end up playing shots when the shuttle is level with or behind me – I could still play decent clears/drops from there, but I couldn't smash with enough power to force a weak reply, and that lead to almost a chain-reaction of problems.
Anyway, my simple solution (at least for now) has been to shift my base back by quite a long way, including standing further back when serving and receiving serve.
I'm now in position to play a powerful smash, right from the very first lift/clear/serve (which seems to be easier than trying to create an opening during the middle of a point).

Obviously this means I have to work a little harder to get to the net early, but it seems to be do-able. I just have to smash and *immediately* tell myself to CHARGE the net (rather than waiting to see what the opponent does). It's probably one of those things where it would help to have a coach feeding lifts for me to smash, and then shouting “GO! GO! GO!”, until it becomes second nature.
Anyhow, it seems to be working (at least for 2 games, and then I'm too knackered) – I just smash and charge at almost every opportunity, and much of the time I get a weak reply that I can kill from the net/midcourt. If they're able to hit a deep lift and I'm already too far forward to get back and smash, then I just clear/drop and go back to playing from my deep base position until they lift again.
It's not what I call “proper” singles play, but it's *very* satisfying when it goes right, and so far it's been pretty effective.

The real test will come next week, when I play some people I know are a fair bit better than me.
I just need to remember to wait further back, and then adopt the mindset of getting to the net FAST.

ps. Sorry for the overly long post.