@MissBax I am sorry to hear this.
My dd was not a good sleeper and she co-slept. If you choose to co-sleep look it all up on the NCT website or elsewhere to ensure it is all safe.
I think in your shoes I would see the GP because not being able to sleep for longer than a few hours doesn't seem to be normal at one year old. It might be something like digestive problems, teething problems, i don't know but I am assuming you asked for help in the early days, didn't get anywhere and have not been back top GP since? I'm only assuming this because if you were talking to the GP or health visitor you may have mentioned it.
I;m also wondering if maybe you have a touch of baby blues or post natal depression brought on by sleep deprivation, and I would investigate this.
Although I was not a big fan of baby training etc I think in your shoes I would try it, I'd read up a bit, get advice.
Really black out the windows in the bedroom and reassure your dc you are there but won't be picking them up etc after bed time.
re "The constant mess" can your dp/dh help with this if you are doing all the night time duties, could you afford some help in just occasionally.
"...the groundhog day and sheer repetitiveness of it." Do you have any plans to return to work full or part-time?
I know some people don't want to, but I think for some people being at home all the time is just very hard.
You sound at the end of your tether and I am so sorry because it can be so hard.
Please do speak to your health visitor or GP and keep talking to them until you get some help.
Plus maybe try this book, it may hlp. www.amazon.co.uk/No-Cry-Sleep-Solution-Gentle-Through/dp/0071381392/ref=sr_1_1?keywords=the+no+cry+sleep+solution&tag=mumsnetforum-21&ie=UTF8&qid=1528070275&sr=8-1