I think the question about what you'll be left with after a WLE is one for your surgeon, but I don't think they'd offer it if they didn't think you would get a reasonable cosmetic outcome. That's what they told me anyway. I was fairly well endowed, but had a big area, 5cm, so they said it was up to me to choose between a WLE and a mastectomy. I did have a WLE, and didn't get clear margins. But to be honest, it was okay having a 're excision, I didn't find either operation too bad, and was pretty quickly back to normal.
As for what I was left with, its fine, I have scars but they're not noticeable. I had high grade DCIS so not having surgery wasn't really an option, I also had radiotherapy and tamoxifen.
I can recommend a book about DCIS if you think more information would help. I wish I'd had it at the time. It has useful sections on the pros and cons of the various options. It's called DCIS of the Breast, Taking Control by John Boyages, and it's available from Amazon.
Good luck with your decision, I hope everything goes well for you.