Not had time to read whole thread but just wanted to post as I've so often had great advice here that I just want to add my two pence worth (FWIW, DD is 10m and still a diabolical sleeper, she was fairly bad before the 17w regression and we have never recovered...)
BUT if it gives anyone hope (can't believe I'm trying to offer hope because as I say we're still not exactly great, we're just very very very slowly getting into a better state) - Naps improved out of nowhere at about 7m. God knows why. I did some wake-to-sleep for a few weeks before that but it wasn't showing all that much effect. Then quite suddenly - bam - she went from catnaps to proper, easily identifiable long naps, morning, after lunch and until a month ago a brief one mid-pm. So if anyone has dire nappers, take heart!!!
My advice fwiw on multiple wake-ups is just to do whatever you have to do to get through - I was ADAMANT that DD would never co-sleep with us... until one night leaning over the cot AGAIN at 7m when I hauled her into bed with me. Yes, I miss having DH there (he's in the spare room). Yes, I do have mild panics every time I think about it that she will just expect this every night until she's 3 or 4... BUT it's got me a bit more sleep, so I have stayed sane. I think you can only ever do what will help right now, I just don't think it helps or works to worry too much about the medium or long term. Sleep is VITAL, if getting baby into bed with you at 2 in the morning gets you even a couple of hours extra, I really do think it's worth it. And I was sooooo anti the whole idea a few months ago.
Getting the naps right and co-sleeping have really taken the edge off for me... just hope things improve for everyone - we're still in Sleep hell in many ways - I would kill for a 5 or 6 hour stretch - but it's become manageableish and not so overwhelming.
Also, finally, I honestly don't think it's worth panicking about the regressions because these blasted babies seem to change every five minutes anyway, usually with no rhyme or reason. I'm the last person to be Zen myself but I am trying to preach zen-ness, cos I just don't see any other way of getting through it!!!
for you all, I do think it helps to talk on here and NOT to listen to smug mothers-of-sleepers in RL.
THEY LIE btw... :)