Choco I typed you a long reply and lost it -dunno why! Maybe he internet crashed under my sling enthusiasm?!
We are slingaholics (lived in a 3 storey walkup for part of DS's life, but mainly he just loved being in them) and we have 2 main slings we used (out of 4 bought/given to us).
I nursed in the "Lightly Padded Maya Wrap" - only one I could nurse in, but very very simple to use. To be frank I have large breasts and a short back, so they hang quite low on me, and I could never have nursed DS in something where he was sitting up. We also have and love ( and still use, in the backpack style) the Ergo. I have a friend with small, perky, high-up breasts and a normal-length back who nursed happily in the ergo for months. I was dead jealous but it was completely logistically impossible for me! :) However the ergo was dead good as it is very comfy for us (weight on your hips not back -important when you have giant babies, as I seem to do!) and for DS (Legs like a frog when he was a newborn and then splayed as a child - better for his legs, hips and spine than the high-street crotch-danglers. Avoid those ones!
Neither the ergo nor the Maya wrap ring sling are cheap BUT there's a sound second hand market for them on ebay and at sling meets. If you google sling meets uk you'll find one - on FB too I think - and you can go and try some on and pick them up and stare at them and stuff. They don't seem to have them in the US and I was v.jealous. The sling topic here is good too but they will make you want to buy more slings :)
Right, DS has gone to bed at LAST (why, oh why did we take the side off the cot?) and I think I might go to bed myself with a nice book. It's nearly 9pm after all, and I've got that rock 'n' roll life style to maintain!
I hope you have a lovely weekend!