Nipple sheilds saved my bf life! I have 'more flat than not' (!) nipples and tho Caty could latch on she wouldn't stay on and after about 4 rather stressful days of having a midwife out and Caty losing weight she finally said -well, it's a long shot and I don't think it will work, but maybe try some nipple shields - and WOOOHOO it worked.
I used the Medela ones, they look like a mexican hat, they were hard to get as a lot of chemists don't sell them. They were quite good at staying on. I always had a super super supply of milk so I don't think the sheilds affected that, however it's kinda early days in my bf life so not sure what the long term affect would have been.

In saying all of that, I was finally able to ditch them about four days ago for good! Or rather, all feeds except the first one of the day as my boobs are quite full and my nipples are more flat than usual.

I think using them helped my nipples to 'come out' a little as since ditching the sheilds my nipples seem a bit longer - not that I'm getting the measuring tape out!

Good luck with whatever happens....they may have a bad rap but they certainly saved me from havign to express into a bottle each and every day (not that that's a bad thing at all!).

Sorry about the long post!