Vest under top works well, although it's easiest with a looser top and I don't find that as flattering on my figure (enormo boobs so relatively small waist).
Vest and cardy can work well - button up top of cardy and pull up, vest down.
M&S do vests in a range of colours with a pretty lace trim for 2 for £8. I now have about 8...
I love these H&M tops tablet.hm.com/gb/product/03578#article=03578-B -
They have them in a few colours, I find them v easy to keep covered up in.
These ones www.mamafeelsgood.com/nursing-tops/ are only very slightly easier than top with a vest top underneath, but the designs are quite young and funky and make me feel less bosomy and frumpy, so worth considering.
And at the weekend I was at a wedding. Wore a v neck jersey dress, had a shawl which matched my accessories in the pram, when the time came to feed unhooked bra, pulled out boob (always a harder part of the process than it's meant to be), then pulled down dress with the shawl draped over. I could latch baby on like this and then move the shawl so it was covering any remaining exposed bits but not baby's face. Muslin also works for this. And if you're booby when not bf'ing, suspect you may already have more than one item of clothing with a jersey v neck...
My baby's 7 weeks old and I'm currently a 38HH - I've fed in public quite a lot and not really flashed anyone yet! I also find doing what I can to make sure baby doesn't fuss/pull off helps - so feeding before she gets v hungry, and changing her nappy first to wake her up if she's sleepy. It all feels so much easier and subtler if you're not wrestling a screaming baby as well as two layers of clothing and a terrifyingly engineered nursing bra - but it took me a bit longer to get to know her enough to do this, and I'm not completely there.
Novel length post, sorry...