Thanks for the replies and suggestions. Heating the cot worked well when she was tiny, but it's so damn hot in the bedroom that this isn't needed at the moment! It's not so much hitting the mattress that wakes her now, it's moving her away from me and down towards the cot. She's ridiculously sensitive to motion - even lifting her out of the car in her seat often wakes her. I always wait until she's properly floppy but it doesn't seem to make a difference any more. Little moves, like from my lap onto the sofa next to me can be achieved with a little stirring, but that doesn't really help as then I'm still pinned to the sofa to keep an eye on her (never thought I'd be complaining about enforced laziness
). I think part of the problem is that she's now bigger relative to my hands/arms that she gets a little uncomfy when I manoeuvre her into the put-down position.
Winding: yes, she's winded, definitely don't think this is part of the problem.
Reflux: don't think so. She's a fairly sicky baby but never shows any sign of agitation with it, and is really very contented when she's not tired (which she often is as she refuses to fall asleep, the silly little thing). She's very happy on her back awake or when asleep, so I don't think it's discomfort. As I say, this isn't a frequent waking problem, she'll go 10 hours overnight (and presumably self-settle a few times during this which confuses me a bit as to how she can manage it overnight but not when going to sleep?) it's a settling to sleep problem and/or inability to get her into the cot once asleep.
Sling: ahhhh I had such hopes! I could get her into it once she was asleep with some stirring but then going off again (haven't tried recently to be fair) and she'd stay asleep for ages. But trying to get her into it when not asleep is like wrestling an octopus! She just hates it, and would definitely not drop off in it. I wonder if part of the problem is that she's so curious (doesn't really like staring at me too much, hugely prefers to be held facing outward so she can see the world) and wont fall to sleep without help as the world is too interesting. I've obviously tried to make the bedroom as non-stimulating as possible but makes no difference.
Cosleeping: I feel really nervous about this for some reason, and DH is dead against it too. Catching up on sleep is only needed if I end up having to cuddle her for hours a night when I can't put her down.
Anyhow, a couple of nights later it's getting a bit better. She basically really needs to suck something to get her to sleep, and we've found that if we put her in the cot very tired but not actually dropping to sleep (when we did this the waking up would make her very upset and she'd cry herself awake) then give her something to suck (still hit and miss on the dummy, but a finger is working OK) then she's doing a lot better. It's still taking an age for her to get to sleep, but there is much much less crying which is good.