In the end, I decided to use a cotton voile for the lining, and attached the gathered tulle about a quarter of the way up from the bottom of the lining (so that there would be something between the tulle and my legs). The lining was then hemmed half a centimetre shorter than the outer skirt so that it wouldn't be seen under the exposed part of the tulle.
I ended up using a metal jean zipper as I realised at the last minute that it was the only one I had here that was long enough. That worked out ok, as I it exposed and didn't sew across the metal teeth like I normally do. It seems popular to sew the zipper tape for these to the outside of garments at the moment.I have no idea why, because it makes it look like someone's made a stuff-up.
I wanted to sew a feature bow as well, but for the time-being I'm just using this ribbon I had lying around. I think it works well in any case.
I might make a few more tulle skirts. It takes twice as long (as you're effectively sewing two skirts together), but I think the result is worth it.